I don't know how much it cost, but I read a story once about a United 747 captain chartering one for his retirement party! They took off from SFO or LAX, flew over the Grand Canyon, up into Oregon/Washington, then back. The FO and cabin crew donated their time. Everyone pitched in a couple hundred bucks for drinks and the charter and they actually ended up with extra!
Cool way to finish a great career, huh?