If you want to make sure you get the money you want, collect it at the door.
So in the invitations say that you're having a part at X time and place, the cost of admission is $10, and people can buy tickets from you in advance, or pay at the door. Then hire someone to collect tickets at the door of the hall. This makes it clear that you're holding a paid event.
Seriously, hire some goon to make sure my 12 friends pay before they enter the premises?? I'm not sure that's the kind of party I want to have ...
I refuse to think of it as buying tickets for a party. It's not the Met Ball - it's a get-together for 12-15 friends.
And thank you to those of you agreeing with me that it feels off-putting to ask advice on X and be critizised for Y.
In any event, even if Jane and John felt strongly about the "admission fee" (and I know they don't, as it is normal here!!), their choice not to pay could be labeled as retaliatory rudeness, could it not?
If someone invited you to something you thought was rude, would you show up and just not abide by the rules?
Anyway, party is canceled in 2013 and a new party will arise.