So what will your badge cover for "free"- All Dealers Hall Demos (enough of these going on to keep you busy the whole weekend), The costume contest, all seminars, Cardhalla (yo can build anything you want using old cards), the Ennie Awards ceremony, Most of the film and Anime Screenings (there aren't a lot listed but will start fill up after the the opening event rush next Sunday).
Most board games and RPGS will run on a $2 for $2 a hour rate but check the prices... some GM's will add some extra cost in to cover extra props, or prizes for the game or just to turn a little prophet. The basic 1$ dollar an hour cost is to cover Gen Con's rentals fees. (the money Gen Con pays out for table, chair, and table coverings)
Other events like True Dungeon or the Escape rooms will charge a larger fee to cover prophets or make a buck.
Origins in Columbus runs on a similar model with the play to pay format. Since thosse are the 2 main conventions I go to I'm kind of used to it.