I ordered one of these custom T-shirts. A bit pricy, but it appears that this site works with independent graphic designers, so there's 2 layers of profits built in to the price. They custom print (1-off each time) as orders come in, so no economy of scale either.

They do have a 10% off feature, using discount code at check-out.

The discount code is: moon10

Watch for me at next year's convention . I'll have it at the SuperShow in February too, if I can make it.