I can think of two right off the top of my head.
1) The robot. You've got one in the storage room. Get some poof balls and a corner goal, and make up some sort of challenge. (Whoever rounds up the most poof balls in one minute over the course of a lunch period, say, gets a T-shirt.) Batteries might become an issue, as will wear and tear, but you should be able to rack up some considerable cash this way.
2) Mini golf. It's been done before, so build a few holes (or even one), get some balls and clubs, and let folks take a swing at things (literally).
There's plenty of ways to get the money; you've just got to be creative about it.