When I first started screen printing, I just had a frame, and a piece of plywood that I would shove inside the shirt. It worked, but not great. Later, I found plans for a 4 color screen printing machine listed on ebay. I invested the five or ten bucks, and bought them. I built the screen printing machine, though I had to modify the design some. I have been using it ever since. I have only ever done single color printing with it though. If I had better screens, maybe screens with aluminum frames, I might try multiple color. But for the most part, single color printing is mostly what I want to do anyway. And the screen printing press I built worked fine for that.

If you are going to be printing many t-shirts, I seriously recommend that you look at screen printing machines. The benefit of screen printing machines is that you can slide the t shirts onto the board and they will be positioned the same everytime. Also when you drop the screen onto the shirt, the screen won’t move, giving you cleaner results. Also, if the ink didn’t get good coverage, you can drop the screen back onto the shirt, and do another pass and have a shot of getting a good shirt. If you have a loose screen, and don’t get good ink coverage, forget it. Just throw the shirt away. So a screen printing machine will save you money on wasted shirts, and give you better results.

I found that Dick Blick sells a bunch of screen printing machines, including a single color screen printing machine probably for less than what I built mine for. I wish I had seen that before I built mine.
They ever sell some really cool higher end screen printing machines such as the Dynamic 4-Color Screen Printer and the Jennings Professional 1-Color Press.