Dude best party investment you can make. I know two kids with tattoo guns, and let me tell you, kids end up with hilarious tattoos the morning after parties.
just make sure you don't give anybody else a tattoo until you are well versed in the art, practice practice practice, you can get pig skin from a local butcher, its really similar to human flesh, and then when you are decent on that start working on your own body, easiest to do thighs and lower legs. If you want a cheap one, get to know the people at your local tattoo shops, if you have a bit of patience, you can get a used gun from an artist who is upgrading or just switching up to a different gun. just make sure to order a ton of needles and never reuse them.