What are some detailed plans for making a t-shirt cannon?

I am the spirit director for my school and need some plans to make a t-shirt cannon! If you know a site where they sell reasonably priced ones, please let me know. We're on a really tight budget but i think it'll be awesome if we get one.

Many T-Shirt Cannons do cost a pretty penny. Personaly, I reccomend building one. They can be safer and sometimes higher quality and, because they are built custom, they can better suit a particular need. (i.e one made of ABS plastic for higher pressure.

There is a link to some plans at
http://blog.makezine.com/archive/2009/01/maker_workshop_burrito_blaster.html