I helped motivate myself to quit a bad habit once with magazines. They cost under $5 and I love magazines, so it was great to have a chance to treat myself to whatever looked good and sit and enjoy it with a glass of tea after meeting goals for the week. Not everyone loves magazines like I do, but it worked for me - travel mags, cooking mags, ATlantic, Harper's, New Yorker, Utne, even random ones that looked good like surfing or photo mags. Go to a well-stocked newsstand or bookstore and have a browse.

I don't know if you can stand stuff like Claire's, or wear that stuff, but many earrings/headbands/barrettes etc. run about that cost.

What about tea? ARe you a tea drinker? Would special tea work?

What about time? Can you have your SO agree to set aside 2-3 hours of me time where you have the house to yourself for a movie and bath or something like that?

Museum membership (for building up to, of course)?

Music downloads?

My next self-reward is going to be a manicure/pedicure. Just manicure would be within your price range, I think?

Fun/warm/comfy socks?

How about a tip jar for yourself, and pay in a dollar per mile, and a dollar per 30 minutes or half hour doing some other exercise. Then go spend the accumulated cash -- spa experiences are always wonderful.

Also, you can log your workouts on a website that will pay cash to charity of your choice.

I find both very motivating.

Fancy candles that smell good?

OK, these are all great ideas! I like the idea of tea, especially.

It's not exercise related though. I don't need external motivation to exercise anymore :) Just motivation for oh, nearly everything else in life.

I say go with books. You know you're going to buy books, but you can use them as a reward, and buy an extra book, or a book a bit beyond your price range as a reward. Also, a note on your calendar helps, too.

Kind of embarrassing but ...cheap game apps or Steam downloads, and then the NEXT reward is like 20 min of playing time.

Some of the small-to-medium treats I've allotted myself for Health Month, both as rewards for completed months and as my now-required Daily Act of Self-Care:

- a bottle of nice lotion, and the assignment to use it (Yes, it's embarrassing that I had to make it an assignment, but that's how it is with me.)
- the ginger ale cologne from Demeter
- new nail polish
- time set aside during a busy day for some small act of self-care: taking a long bath, painting my nails, meeting with friends
- a bottle of The Good Rum
- a packet of vanilla beans
- a trip to the awesome used book store with one assignment: spend $__ on books just for me
- an afternoon at the museum
- new pillowcases
- new socks or tights
- new art supplies, beading supplies
- noir movie marathon with a friend
- new kitchen tools
- a REALLY GREAT new metal nail file, OH HOW GREAT I AM SO HAPPY

I haven't yet indulged in all of these, but I had such trouble thinking up ideas that I now try to keep an actual list handy in case I need it.

Some ideas I'm going to use in the future:
- new (cheap!) glassware; I loooooove specialty glassware but am usually too miserly to buy them
- music: downloads or from our local record store
- new cabinet pulls
- new tools or stocking up on screws and nails (Do you love adding stuff to your toolbox? Just me?)

This one doesn't translate, but bear with me: I make beaded jewelry, but I end up wearing the same few pairs of earrings all the time. So one night I sat down and made myself several pairs of new earrings. Do you have some comparable skill, something that you usually use for friends or family but rarely for yourself? Do it for yourself.

socks. sockssockssockssockssocks!!! I dunno about you but I go through socks at a ridonkulous rate. Even if I'm super duper careful I still wear through socks in a season. And new nice ones are one of my giddy little pleasures.

side note: has anyone else noticed that the quality of smartwools has dramatically fallen off of late? Seems mine wear out after about six months these days. And I'm not talking just holes (no, I darn those). I'm talking wearing thru paper thin / translucent at the toes and heels. Just me? ok.

I feel like I've clicker trained myself with cough drops. I know you said not food but I don't know if other little things like altoids or mints or gum are the same sort of thing. For me they fulfill the "want something strong tasting, want snack" feeling without actually eating something not good for me. So I'd put a cough drop in my pocket and only have it after I'd gotten to the recycling center or gotten the snow off the car or gotten the dishes done. I've also found stuff like really good moisturizers, especially this time of year, are a good incentive. "I'll go do this thing and then I'll give myself a peppermint foot rub" or "I'll do this thing and then do a face mask thingie" And I know you said you're okay getting exercise but I have found that having a show I only watch when (or after) I do a thing I'm not that stoked about is helpful. So Downton Abbey while on the treadmill, or finishing up that movie after I've finished making dinner or made that annoying phone call. See also: cocoa with or without shots of really uneccessary liquor ( I have some of that whipped vodka which is ridiculous and yet very good in coffee)

I have found that having a show I only watch when (or after) I do a thing I'm not that stoked about is helpful.

I do this with podcasts, too, though not necessarily for exercise. I can only listen to the newest RadioLab while I'm cleaning or organizing or otherwise doing household busywork, for example.

It's funny, because if I'm going to blow $5-10 on something for the sake of blowing it, it's a Lush bath bomb. Use to be a coffee drink, because that is such a pointless waste of cash. Even cheaper, trying unknown random beverages, because I'm not a big beverage person unless it comes with a vitamin, mineral or chemical. So while I like teas and I'll have a water with my water, besides that, beverages aren't usually reliably satisfying. Actually, few things are unless I've kind of conditioned my response.

If the treat is the pointless blowing of money, which I pretty much don't do, then I will go with something really unnecessary, like quality cosmetics/grooming supplies, but that's over your price range. Does anyone really need liquid gold eyeliner? Ya know, I'm pretty confident I can find a logical rational for it, if need be.

Because I don't blow small sums of money, when I blow money at all, it's to a set limit, whether it's thirty bucks or three hundred, but there is usually a point, whether it's embroidery thread or a pile of feathers, copper wire, adding to a decent wardrobe, some rare pigment, tools-- that pile of glittery whatdawhozits is not just for rolling around it, it's probably part of something.

Okay so for more normal people who would not be looking for giant spools of telephone wire or rectangles of frosted plastic, more necessary, usable items:

nice stationery items: fine/interesting cards, paper, envelopes, stamps, tape, paper clips, etc. There's some surprisingly innovative, fun little things out there. Also, pens and pencils. Are there still stationery stores? Does anyone remember them? I loved those places. Back when people collected stickers, I had a crazy awesome sticker collection. And erasers that smelled good, pencil boxes...

underwear and hosiery: not like La Perla, but reasonable, attractive, functional panties or some cool stockings or socks. Or goofy, goofy is fun.

fun accessories you don't have to be that worried about losing: I don't know about you, but it is freaking freezing out here and I'm always having to check that I haven't lost good gloves or a scarf I really like, etc. Plus, unless you have a variety of outerwear, people usually look mostly the same most of the winter. It is hat season and people love hats on other people. More of an investment, but a good hat is really worth it. Note: depending on where you live, some people see an interesting hat, or, really, anything interesting/unusual on your head, as an excuse to interact with to you. Some people like this, some really don't. I'd often forget I was wearing cat ears to keep my hair out of my face and wonder why people kept stopping me on the way back and forth from the laundry, etc.

novel kitchen wear: you use to be able to get these little glasses, basically like cool shot glasses, longer, thinner, different shapes, etc. and you could use them for shots, soup, bud vases, arrangements of colored water, whatever. An interesting spoon or fork. A whisk that looks like a squid. etc. John Allison tea towels. A spoon rest. And the list goes on.

unfamiliar herbs and spices. Exotic salt or that sumac mix I haven't been able to find for 15 years. Or condiments, if that's not crossing the food line.

zines and comic books.

essential oils and scents.

flowers, with scent and you can scent a room.

ornaments, toys, miniatures. Tiny fake food! Miniature plastic hippos! Plush ninjas! Germs!

I was making a list for everyone but I just remembered you are in New York.
See, I think if you find anything that gives you actual, genuine, reliable pleasure, satisfaction or delight, especially if it has little to no downside, you should have that thing because there really isn't much of that in the world if you've been around a while, really looked around, or bore easily.
How about instead of money or a thing, you give yourself time? Maybe it's time to look for a thing, but you are in one of the few places where you could find a wide variety of interesting, new, old, unique and/or relatively inexpensive things or sights within a small distance. You could probably not only find a stationery store, but the best or hippest or weirdest. One day, you could look for scents and find the best, cheapest scent store. Another day, the weirdest little mechanical toy in Chinatown. Another day, the best Middle Eastern spice shop or arcane amulets or mood rings. And if you don't want to accumulate stuff, get them as future gifts for people in particular or at random. I love getting things for other people, especially if they can really appreciate them, but random little gift giving is an interesting thing I'll go on about at another time.
Unless New York is so different now it doesn't resemble my experiences any more or you don't like shopping or going out, in which case you could have almost anything delivered or shipped. But if you like going out, I can think of a handful of tea shops offhand, or wander around some cool boutiques or galleries and find stuff you love that you didn't know existed. Did they get rid of curio shops and junk stores and vintage places or is everything ridiculously inflated in price now? No more flea markets or used stores? Don't you have the last real seltzer water guy out there and the best pickles [no calories stuff]? Can't you just see and find stuff there that isn't anywhere else?
Except for the weather, I'd probably just wander around if I had the time, but like I said maybe it is drastically different now and there aren't little niche shops anymore and you're not allowed to just wander around Bergdorf's or Barneys or wherever while they give you tea and wine. I mean, I'm pretty damn sure that store down Broadway with the grand piano and all the live animals is definitely gone, if it wasn't some experiment or drug front anyway... well, now, I'm kind of sad.

One of the few things my mother ever did for me, albeit accidentally, was show me that there was a vast array of stuff in the world, whether it was a fresh seafood market where she'd test if the crabs would grab for a quarter or some giant flowering plant store, probably giant because I was only single digits, or department stores... when I was older, there were little hole in the wall punky shops and innovative housewares stores, sample sales and dingy comic shops, some store with nothing but wigs or glass doorknobs or magical herbs or places with every kind of item in certain category. The place was always changing, but I could see all those little weird shops dying off for good, with rents, deaths, the economy, the internet... gah, what if in the future they don't even have shops anymore and it's all just warehouse stores and online orders unless you're rich?

Now this is what happens when you have an early day, have a couple glasses of wine with a meal, nap, wake up at 1am and start chattering on the internet: you realize New York may end up all Disney and Guy Fieri and showcase boutiques and chain stores... basically expensive Las Vegas. I think I need a taco and to go back to watching Angels in America.
Damn you, Vonnegut. We should have never swapped states.