If you don't already have them and you're looking to spend money, I recommend 3 card monte and / or color monte. I think each is only like $10, so you could save some money and still get a couple nice tricks. You could always bet people a dollar and make the money back over time too.
I once got 7 free drinks in one night just flipping past a guy's card and betting him the next card I flipped over was his. I think that 80% of everyone knows how that trick is done though, so I came up with a version to show them how it's done (seeing 1 guy in a crowd will yell out they know anyways), but the demonstration is actually a setup for another trick. In the end, you end up pretending to take it easy on them by betting them again that the card you plainly put on the table is their card (by showing them an indifferent card), and they assume you're "buying back" for the last drink / bet. In the end, you're just getting them a 2nd time.