The A-10 Thunderbolt - $212 million
This plane, better known as a Warthog, provides support to ground troops in combat. But it's slow and prone to maintenance problems. The Air Force has been trying to retire the plane for years, but Congress has repeatedly stepped in to save it. The latest effort comes from the Senate, which included a provision in the 2014 defense authorization bill prohibiting the Air Force from getting rid of the plane until 2014.
