My own urine after a hard night of drinking, I bottle it and sell it on ebay for $54. I know it sounds expensive but all I drink is top dollar vodka and tequila.
Taft is right most people on here myself included use the gift of the magi to clean (lightly sand) off tough stains. I do also use the exquisite cleaner that was peddled here on WW and Babes. For tough stains I've also use good ol'fashion UV rays from the sun.