I've been screen printing my shirts lately go
here for a really nice tutorial. even though making the screen takes time if there is a lot of detail when it's done you can make as many shirts as you want very easily.
i like this process because you don't have to worry about buying minimum amounts like some printing store have. and depending on what kind of shirt you buy, it ends up only costing a couple of dollars a shirt. once you start getting good with it, you can starting using mutiple colors by layering the screens.
i hope this helps.