Sturgis Rally & Rapid City SD

As a last minute decision I am interested in attending the AMA Pro Flatrack 1/2 mile race Aug 4th durning the world famous Sturgis rally. Has anyone here got any ideas or place at this late date I might find a campground near Rapid City ? It needs to be close to Rapid City because after the night race is over at 11pm I don't wish to ride far with all the critters ! I have been looking and came up with nothing and the motels are all booked with even Motel 6 getting crazy prices, Super 8 wants between $219-329.00 per night. Nothing like good ole screwing but I guess their season is short and you gotta make it when you can.