I was wondering if there was a way to use KickStarter.com to handle the business side of things. The reward would be the t-shirt and you would insulate yourself from risk.
I found this site http://yque.com/tshirtprinting2.html that gives a starting point on what it would cost.
I was also thinking about how you could use Amazon's fulfillment service. It would cut into profits but save some hassles.
I was thinking, use KickStarter for a 2 week run with a goal that would be sort of a breakeven profitability mark (using those costs above). If it doesn't hit the goal, you cancel orders. If it does, you order the shirts from a place like the link above and have them drop shipped to Amazon for fulfillment and then have them sent out.
You have to consider the materials of the t-shirts used, seems like most of the folks like t-shirts printed using American Apparel t-shirts.
I'll be relaunching the site soon. It's great to be finally working on my own startup.