I'm a new yorkie mom, and I have a small pup named Joey Buttons. Although he wasn't advertised as "teacup," he is very small (only 3.5 lbs at 6 months old) and is only expected to grow to 4-5 lbs.
Vet bills for Joey were quite expensive to start. He's so small that he can only handle 1 shot per visit (as opposed to 2) so we had to take him to the vet almost every other week for a while. I live in NYC, so the prices are probably more than what you're looking at- but I definitely spent $1000 on all the shots and vaccines. Now he's done with shots, we're in the clear until next year! (Thank God!!)
Additionally, he got a bit of a belly ache a few weeks ago, which I'm told is quite common for pups, so that was another couple hundred for a vet visit and a week's worth of medicine. (They're just like kids during the first year in school- they'll pick up whatever is in the air!)
I haven't neutered yet, and I'm not 100% sure I will. He's so small that at this point, I don't want to do anything that would stunt his growth or deter him from eating.
The other thing that I would consider mandatory is grooming. These yorkies have long hair! I would think prices vary drastically on this one, and if you can do it yourself- I would!
Having said all that, check out Joey's breeder's website if you're near PA:
Ellie's Cute as a Button Yorkies. Joey is THE BEST puppy I've ever met0- so well behaved, super smart, and SOSOSOSOSO cute!! I would whole-heartedly recommend purchasing from Scarlett and Amy. I hear they're having a litter in October!
Good luck!
Edit: Just saw you're from Toronto, so that's probably too far for the breeder I purchased from. Good luck either way! I found my breeder in the local paper and when I called, she asked more questions of us than we did of the puppies. I saw this as a green flag- she obviously wasn't going to sell to just anybody! She basically interviewed us LOL (thankfully, we passed!)