Here are a few sources for cheap Obama T-shirts.
Three different Obama shirts are $10 each (orig $15) at Spencer’s.
At BCheap patriotic Obama shirts start at $13.
A shirt with a D.C. license plate that says “OBAMA” is $13 (orig $22) at Karmaloop.
“Obama is my homeboy” shirts starts at $20 on this site.
If you live in a major city, street vendors may be even cheaper. In LA, head to the Fashion District. In NYC, head to the Garment District in the 20s near 8th Avenue.
Remember to haggle! If you are buying in bulk or buying odd sizes they might not otherwise sell, you have more leverage.
If your politics swing the other way or you are trying to piss off the rest of the country, “Obama sucks” T-shirts are $16 at Funny T-shirts Inc.