The sale of jersey numbers is a time-honored tradition in sports. A team will sign or trade for a star free-agent, and some other scrub on the roster is already wearing the number that said star has worn his entire career ... and the star will pay the scrub tens of thousands of dollars for his number, allowing the scrub to be anonymous in some other number while spending the cash on booze, drugs, and if he's anything like Plaxico Burress, sex. That's what I'd do.
Jason Simmons of the Houston Texans, though, is a better person than I am. He's worn #30 for the Texans for as long as the Texans have existed. The team brought in Ahman Green from Green Bay, though, and Green's always worn #30. Simmons was in line for a payday, but instead, in return for the #30, is having Ahman Green make the down payment on a home for a disadvantaged single parent. Jason Simmons is a sweet, sweet man.
The best "jersey number for sale" story of all-time involves Clinton Portis and the #26. When Portis was traded to Washington, 26 was worn by Ifeanyi Ohalete. They worked out a $30,000 payment, signed a contract and everything. Then Ohalete was cut, and Portis refused to pay. Ohalete kept nagging him about it, Portis suggested they settle things with a boxing match, and Ohalete sued him. He did eventually get his money.