Well, for starters, all the commercial & ATP pilots who fly in the air show get gratis fuel & smoke oil. I counted dozens and dozens of warbirds who flew daily at AirVenture. Ever thought about how much gas it takes to put on the air show? Even though no one gets paid to fly in the show (like they would at other air shows), everyone does get free fuel, funded by admission fees. How about the Forum facilities, port-a-johns, showers, trash service, water bulls, buses & bus drivers (they're not volunteers), etc, etc. It's really only because there are so many volunteers that the price is so low.
Personally, I think AirVenture is a GREAT deal and I was happy to pay $107 for a weekly pass.