If you want it yesterday.
You make virtually nothing, under $1 per shirt. they will print everything, the quality is substandard. I've used them over a dozen times.
Source a local screen printing shop for good quality 100% cotton (I prefer Gildan) t-shirts. Take a look at their equipment, and then look at the price difference. Watch how much care they take in printing the screens. I have been sourcing locally for the last 3 years, and my original order is still holding up after 40+ washes and the colors haven't cracked at all or faded too terribly.
From my experience, a cafepress t-shirt will fade and crack after 3 or 4 washes.
Locally, I paid $350 for an order of 100 shirts printed, 3 colors, front and back, and sold them for $10-15 apiece.