Definitely watch out for any one trying to sell you a 'tea cup' Yorkie. It's a marketing scam, and they try to charge more, or make it sound special... really a Yorkie is a Yorkie. There is no such thing as Teacups. The yorkie standard is 7lbs and under and they are a breed in the Toy category.
Check the Yorkie Club of America for a list of good breeders.
Yorkshire Terrier Club of America
or check petfinder.com if you were interested in rescue.