screen printing your own t-shirts.
 

have any of you done it? what's the approximate cost for all the supplies, and would you consider it worth it to do just as a hobby?

It was easier, cheaper, but less impressive and good looking to just spray paint stencils. I used to do it all the time in school.

If you have a decent printer I think you can just buy a certain paper for the screen prints and then iron them onto t-shirts. Supplies shouldn't cost too much, just the printing paper. It does cost more than regular printer paper though. When you iron the designs on just make sure you don't go over any seems. I ironed on a DKM design onto a dress shirt and half of it fell off.

This. Especially if you're just going to do a few, it's not really worth it to invest all the time and money on screenprinting them if you're doing a small run.

Dickblick.com (not a porn site, I promise) sells a pretty decent screen printing kit by Speedball in both a basic and deluxe version. The deluxe version also comes with an instructional DVD.