From FederalTimes.com: For sale: Space shuttles, slightly used, bargain price!

NASA is now selling shuttles Atlantis and Endeavour for $28.8 million - nearly a third less than their original price tag of $42 million. (Shuttle Discovery has been promised to the Smithsonian Air and Space Museum's Udvar-Hazy center in Northern Virginia, which currently houses the Enterprise prototype that never flew into space.)

$28.8 million sounds a lot for a museum piece, but paintings have sold for nearly 5 times more.  Still, it's difficult to imagine that any science/air museum will be able to afford the costs of purchasing and exhibiting a space shuttle in this economy.