Also, the perk price shown in the hangar is a snapshot of the price at the moment you entered the hangar. If you take your time spawning that perk plane, the price could have gone up or down, since the perk price is constantly updated by the game. Once you spawn, the actual perk price is shown in the text buffer. If anything other than a successful landing at a friendly field happens, you will lose a portion (up to all) perks spent at the time you spawned.