The guy I usually use (
http://www.brunettotshirts.com/tshirts.html) can do it for $10 on white or $10.50 on colors with four colors of printing (and on niiice american apparel shirts), but there's a minimum order of 30 for four colors.
If we want to go with that though we could maybe cut a deal to do less -- about how many of us are there?