Have a camper (Igor) stand in front of the audience and the other three stand aside.
The 1st camper walks up to Igor and Igor asks if he wants to buy brains. He asks for some candy and he yells "GO AWAY!"
The 2nd camper walksup to Igor and Igor asks if he wants brains. He asks for soda (any brand) and Igor yells at him again.
The 3rd camper walks up and Igor asks if he wants brains. He agrees.
Igor shows him a Scout's brain (imaginary) and says, "camper brain, 1 dolla', camp counselor, 5 dolla'" He continues up and keeps raising the price all the way to Camp Director's brain for $1,000,000.