What to do in NYC on a Saturday night?

I live in NJ and for my sweet sixteen I want to take 10 to 12 of my friends to NYC at night. We are going to take a limo there and back. First we are going to have dinner, but I don't know what else to do. We can't see a broadway show because it will be too expensive for all of us to go. What else is there to do that isn't too expensive at night?