Ground handling fees were over $400 per landing for a tiny plane in a tiny airport. That's about 25% of the potential revenue, and the biggest total expense, for a 9 seater with a default ticket price under $200. I don't know what ground handling fees pay for IRL. I imagine a lot of what a large plane in a large airport needs (tugs, baggage handling, parking spot) simply isn't required at all by a small plane in a small airport. Possibly just setting any airport size 3 or smaller, visited by any small or even medium plane, to have very low ground handling fees could help with this. Not sure.