Brains For Sale

A man walks into a scientist's lab looking to buy a new brain. He asks the scientist how much the brains cost. The scientist says, "Well first we have a normal human brain, it costs $1000, next we have a scientist's brain, it costs $5000, and then we come to a politician's, it costs $10,000."
"How come the politician's brain costs so much?", asks the man.
The scientist replies, "Because it's never been used."