it all depends on how many shirts you're trying to print.. most shops have a minimum.
which is like 24 shirts sometimes. Some places dont have a minimum but it costs more and it also depends on how many colors because as you know each color costs $.. the more colors the more it's gonna cost.
with that said, the cheapest ive seen so far would be
www.nativegraphixsf.com
and then i just came across a hook up that does ya boy's t shirts and i think he even did that Ya Boy writing we see everywhere.