If you do an internet search for "custom t-shirts" you'll find there are companies that will take your rough sketch and do up the artwork at no charge (but you have to order the shirts from them - duh).

Here's a company I use (for patches, but they also do t-shirts) - I've had nothing but great success with them (and their prices are great - low minimums, too)!

http://stadriemblems.com/tshirts.html

Hope that helps!