The best deals will probaly be local used bikes. Atleast where I live used bikes on sites like ebay are way more expensive than bikes I find at threft shops or classifieds but ebay may be the best option for your size.
If you find you want a new bike i'd suggest look online, Bikesdirect.com, performancebike.com, and ibexbikes.com are good sites also, ebay has some good new bikes.