And if you're in a mission its free to transport you, because the costs are picked up by the country to take you around, but to post a mission with certain planes it costs Mission Perkies, i.e. a NIK mission would need a 20 perkie investment :-), meanwhile a f4u-1 mission would be free of charge to all those who joined. You get mission perkies by joining a mission, or succesfully launching a mission.
Yeah we're onto something now..