I don't remember exactly how much I had budgeted, but I want to say I ended up spending a couple of grand once everything was all said and done. That includes food (drunk munchies add up), hotel (week), etc.
We went out to the "clubs" pretty much every night and those can get expensive if you party like a rock star. Considering you're wasted pretty much the entire time, you spend money a little more frivolously than you would if you were sober.
We also did a lot of stuff like parasailing, bought boogie boards, etc., too, so it's nice to make sure you have money to do lots of fun shit while you're there. That's what it's about - having a care free blast with your friends and hot women....one last hoorah before you all graduate and enter the real world. It's nice to have little financial restraint during the trip. You don't want to look back and have to say you didn't get to do something that would have been an awesome time because you didn't have a few extra bucks.