I've dealt with VistaPrint before, they weren't too bad but that was only for a few shirts here and there. My next move is called "the t-shirt land". On their website you can select different grades of quality, different styles and colors and you'll see the price ranges according to the total number of shirts you want.
Since I haven't used them yet I can't tell you about how good (or bad) they are. I'll know soon.