My chapter will order t-shirts from pretty much anywhere in the nation as long as their rates are cheap. Only things that really matter are the quality of the product and total cost (inc'l shipping).
That said, the cheapest place we found so far was actually this place near my campus (in California) that was really willing to negotiate. However, they really try to be an online-only business for the most part:
http://www.printhero.com
In the past, we've also had great luck with CustomInk, but the prices are kind of expensive:
http://www.customink.com