Like a lot of other people, Bill Rock of Madison wonders why his prescription drugs are so expensive. He suspects itââ?¬â?¢s due in large part to ââ?¬Å?huge mark-upsââ?¬Â; this, he reasons, would account for wide disparities in cost and the fact that providers like Wal-Mart can fill many common prescriptions for as little as $4.