This sounds like a pretty cool idea for a birthday party. But I believe a good T-Shirt machine cost a big amount of money. My brother has a special website where he sells T-shirts. I believe he prints each T-shirt himself with a special T-shirt machine. I don?t really know how much time he spends at his job but he enjoys it pretty much. I helped my brother with the choice of a digital t-shirt printing machine, but we ended up on a cheapest one. I don't really think it?s worth to buy a new T-shirt printing machine just for a birthday party. But it's still a cool idea maybe if you can rent such a machine for one day.