The plane is a McDonnell Douglas DC9-32 that was active between 1975 and 2005. Although it was never the primary presidential ride it did serve as Air Force One on several occasions.
The auction site says:
In the thirty years this aircraft was assigned to the 89th Airlift Wing (Feb 1975-Sep 2005) it flew Presidential missions, Vice President, First Lady, Cabinet Secretaries (Secretary of State, Secretary of Defense, others), Chairman Joint Chiefs of Staff, U.S. Senators, U.S. Representatives, Four-Star Generals, Admirals, Foreign Heads of State and other foreign dignitaries.
The plane is being auctioned off by the feds and the starting bid is pretty low.
Just submit a $50,000 bid deposit and you can be on your way to owning a piece of history.