Fun Prom Ideas on a Budget?

We have booked a beautiful venue for prom and therefore have a TINY budget for everything else. We have food, drinks etc under control but people had been asking for fun ideas such as a photo booth, but i'm not sure our budget will stretch to that. Does anyone have any cheap fun ideas (not games) to make sure it is a fun, unique night. Im thinking along the lines of a screen where people can text in their comments, messages etc. Just as an example of the kind of thing we're thinking of. I would be very grateful if anyone has any cool, unique, cheap ideas to make it an unforgettable evening! Thanks x