If you intend to stay under $350, I think you will have to look at a Rescue, older dog, or an accidental mix.
Try checking some of these:
http://www.yorkierescue.com/ http://adopt-a-yorkie.1-800-save-a-pet.com/ http://flarescue.tripod.com/flrescue.html http://www.yorkshireterrierrescue.net/ http://www.yorkiefriendsrescue.com/
and:
Central Florida Yorkshire Terrier Rescue
Dedicated to the care and well-being of the Yorkshire Terrier, including finding suitable new homes for displaced yorkies, temporary shelter during times of crisis, and rescuing yorkies from hazardous situations. Primarily operating within the central part of Florida from the Gulf Coast to the Space Coast but available to assist other rescue organizations whenever possible. Contact: Nancy Douse, Loxahatchee, FL, Phone: 561/333-3420, Email Address: tattler11@aol.com