Planes get entirely too expensive near the end. I'm 4 planes away from having all of them, but the cost goes up astronomically, and you don't make any more money from completed flights than you did 10 or 12 previous planes ago. The rewards should go up more as you progress and at some point you should get more than just 4 pilots to send on flights for rewards. I like the game, it's just ridiculous how expensive things get, when the rewards don't increase.