Its unlikely if people will pay if it just a case of turning up and getting down. As for making an evening of it, it can be anything. Go simple, make it like a bit of a party, some food, some music and some booze. Have everyone get comfy and then at a pre-determined time you all get down to it
As with any sort of gathering you can charge, but as for what would be acceptable, that would depend on exactly what was on offer. If you can tell me what sort of thing you had in mind I would be happy to give you some guidance