The White House, Secret Service, and Boeing
The White House, the Secret Service, and Boeing are all involved in the development of Air Force One. It must meet Boeing’s quality standards, the Secret Service’s safety requirements, and the White House’s operating efficiency requirements. As can be seen, all three parties are crucial to the remarkable Airforce One.
Source: Wikimedia
The purchase of a plane can only be made during the current President’s second term. Therefore the President cannot utilize the plane they choose.