I agree with the others, and always recommend that people start at the top. It's a common misconception that YTCA members only sell to those who breed or show, for most sell only to pet homes, not other breeders. If you were looking to breed, I would also recommend a YTCA member who could mentor you.
Most people are looking for a great pet, and would like a yorkie that looks like a yorkie, so finding a breeder that understands the importance of breeding to standard is essential. YTCA members are not breeding for profit; they are small hobby/exhibitionist breeders, who understand why showing is important and how this ensures that only those dogs that conform to standard are bred. Breeders tend to look at the own dogs with rose-colored glasses, so having approval of others ensures that you are breeding the best examples of the breed. Prices are extremely competitive because they are not profit motivated, however, requirements for placing a dog are high. Most will require that you be willing to have a dog spayed or neutered before they can be registered, and you must prove that you can provide a suitable home. They will question you on past dogs and your experience with training, but if you think you can offer a good home to a yorkie, this is the best place to start. If you are not interested in a dog that is a great example of the breed, and only want a pet quality yorkie, I strongly suggest you find a rescue, while their dogs may not look like show dogs, they make wonderful pets, and many are already housebroken! This link will give breeder referrals, lots of other good information as well.
Yorkshire Terrier Club of America About The Club