A reputable breeder usually will charge anywhere from $1100.00 to $1500.00 for a pet quality puppy. A good breeder usually rates the quality of their pups as pet, breeder, or show quality.
Avoid people who are selling pups for inflated prices and claiming that they are "teacup," "mini," or some other form of extra small Yorkie. That would not be a "reputable" breeder and could represent someone who may have some questionable stock.
The links given above give some good advise. You can also go to the AKC website and look up AKC sanctioned conformation clubs. They usually have a breeder referral person who can point you in the right direction as far as reputable breeders in your area. Learn the right questions to ask so that you have some background information to lean on when you speak to the breeder.
American Kennel Club - Club Search and Directory
A good breeder will have a lot of background information about the dogs they breed and will be able to show it to you. A good breeding program involves a lot of study in the genetics of the breed and the line they are working with. Genetic testing is really important and hopefully your breeder can show you the tests done and is able to explain what they represent.