check out http://www.zazzle.com/create
I noticed a Google search for: t shirt dropship, brings up a Vistaprints ad for $6.00 shirts.
(it was $4.50 earlier, you should re-try the search now and then to catch sale prices)
THat's about as god a price as I have seen, the premium print on demand services might be good for one off sample printing, the prices at Zazzle.com, cafepress.com, customink.com are considerably higher.
This paid ad appeared under your question (they can change depending on the view so I am repeating it here)
$4.66 each for 24 shirts. Bulk pricing. Free shipping.
Checking heir online quote, you can get white shirts with 1 color printing, 75 pieces @ $3.55