Hi and Welcome to YT! Yorkies are a wonderful breed, no wonder you want one
I think in most places, 500 is on the low end to pay. Sylvan is right, you may want to think about spending more for a well-bred, healthy puppy. I understand about wanting a small pup. I wanted one and got one and he is 3.5# full grown. I can take him anywhere with me and he is adorable. Keep looking throughout this section of the board...many people advertise to sell pups here.
Good luck with your search and I hope you find the pup of your dreams!