Ounces of brain for sale

A man went to a brain store to get some brain to complete a study. He sees a sign remarking on the quality of professional brain offerred at this particular brain store. He begins to question the butcher about the cost of these brains.
"How much does it cost for engineer brain?"
"Three dollars an ounce."
"How much does it cost for programmer brain?"
"Four dollars an ounce."
"How much for lawyer brain?"
"$1,000 an ounce."
"Why is lawyer brain so much more?"
"Do you know how many lawyers we had to kill to get one ounce of brain?"