Brain transplant

So this guy's got a terminal brain tumour and his doctor tells him that the only hope is a brain transplant. "In fact, you're in luck," the doctor tells him: "We've got two brains available, a man's and a woman's. Now, since you're a man, you'll probably want the man's brain, but I have to warn you that it's $200,000."

The man winces and says, "How much for the woman's brain?"

"$200."

"Why so much less?"

"Because it's been used.