That depends on a lot of things not addressed in your post:
Black t-shirt or white t-shirt?
Heavy weight or light weight?
Small design or large design?
One print or two?
Large quantity or small?
Screen printed, sublimated, transfer or
dtg'd?
If screen printed, how many colors?
I just googled cheap t-shirts and found a place that will print 1200 six color shirts for $2.35 each - The shirt is on top of that and if you have to buy from them would run another $2.50 (they make money on the print and the shirt)
Steve