Actually it's not. It's 17.40 base price for the American Apparel shirt (which I made so I could buy, since that's my preference), so it's a $2.60 markup.
It took about 30 minutes to do--and, that long because I had to trace a few glyphs from FF Meta (the font) in Inkscape, since I don't own it. I'd be absolutely thrilled if enough people bought one so that mine is free, but, I'm not expecting that to happen.
The other shirts in that shop were marked up to donate to random open source projects. I think all together, I maybe gave $30-40 away from those sales?
EDIT: I was mistaken. It's a different type of shirt, so the markup is even less!