I second the heat transfer idea. If you're only doing 50+ shirts it wouldn't be worth it to incur the cost of a full screen printing set up. although **** Blick and other such art stores offer small printing setups for pretty cheap. These are DIY kits and are not super high quality but I've seen some people get great prints from barely any equipment.
EDIT:
I see the dirty word filter is set pretty high, here is a link to the art store I'm referring to.
http://www.dickblick.com/