Free: Contests & Raffles.
Make sure you don't run too far up on a shallow beach in the evening. That lake can drop a LOT during the night. It took every boat/watercraft we had, plus the other houseboat to pull it off!
I'd be sure to wait until late July before you go. The lake is required to be "full" at 4th of July which means the beaches are few and far between. Later in the Summer gives a lot more freedom to find the perfect spot, especially if you plan to stay put rather than move everyday.