Everything is negotiable.

This axiom holds true in high-level sports contracts. As The Post’s Andrew Marchand first reported, Fox agreed to let Joe Buck out of his deal one year early to depart to ESPN’s “Monday Night Football” alongside his close friend Troy Aikman. Buck’s wife, Michelle Beisner-Buck, was also already on ESPN’s NFL coverage.

Sports Business Journal’s John Ourand has now reported what ESPN sent back in the swap: the Sept. 1 Penn State-Purdue college football game. Fox stands to make “millions” in extra ad sales from having this game, while ESPN already has a West Virginia-Pittsburgh game they can use in that Thursday evening window.

Trades are uncommon but not unprecedented involving sports media talents. In 2006, Disney’s ABC/ESPN let Al Michaels out of a contract to go to NBC with John Madden, and in return they got the intellectual property rights to Oswald The Lucky Rabbit, a cartoon character created by Walt Disney in 1927.

In 2014, Bill Simmons nearly persuaded ESPN to trade soccer broadcaster Ian Darke to Fox Sports for Katie Nolan. However, the negotiations fell through at the eleventh hour when Fox also wanted Marty Smith included in the deal, and ESPN walked away from the table.