I read a post by mikeslu a minute ago, proposing a way to raise money by making planes act like bombs. Since this would give an unfair advantage to those who pay, I've got a new proposal.
New color schemes for planes. Sold for a dollar or two each, you can buy a new paint job for your favorite plane. They'd be loud and gaudy, so as not to give any unfair advantages (A pale blue planewould be much harder to spot that a pink or yellow one). On second fhought, maybe that wouldn't even matter, on account of the giant names above everyone's plane.
I don't have any doubt that people would buy the schemes, just look at some game that you buy for XBox and Playstation! I could spend over fifty dollars just buying completely worthless paint for my guns in each of my Call of Duty games, but plenty of people still do it!
There could even be bigger upgrades, costing 5-10 dollars, such as having a squad tag printed on your top wing, or your name, or, if you're feeling cocky, your kill count!