I just got the facebook invite for my 10 (my how times have changed).
I grew up in a resort town in the mountains and every class before us has gone white water rafting and then to the local brewery for food and bev.
My class (2000 woot!) is doing a tram ride up to a cavern and then a dinner, all for $25 a person.
Call around to local restaurants and see what kind of "per head" deal you can get. You could do a buffet for a set amount and then have a cash bar or build a couple of drink tickets into the per-head price. There's lots of ways to go around that.
As for what to do, what kind of town are you from? I think I would be mortified to do the typical "let's re-live the misery" and would just rather hang out with the people I grew up with.
On the other hand, I already see everyone I would want to from high school, so I don't know if I would go. We're all trying to talk each other into going