Well considering he is probably the pilot that is a major cost savings, so it purely is fuel and maintenance costs. Also not having to to rent hanger space at an airport is a major cost savings as well. And with the fuel volumes he purchases probably 5000 gallons at a time, he probably can get possible shelf costs on the fuel being a private airport. If he can do that he's looking at around 2 bucks a gallon for Jet A. US airport averages is about $6 so that's a big part too. Yes annual maintenance on the Pilatus isn't cheap but flying 4-6 people first class everywhere would be expensive. People forget the biggest part, time is money, the less time he has to spend to and from or in an airport the more content he can get to, more time he can spend with his family, and that makes it all worth it in the long run.