Right now it's just the economic buildings that have upkeep costs, but I'm going to remove it next update. A few people have had issues with it and I don't want this being a pain point.
Fighter planes should just be in the airstrip, assuming they're in your loadout. The mobile SAM system is a land vehicle. The SAM turret is an upgrade in the base turret. You might be playing an older version, the loadout system was updated somewhat recently so there's a lot more structure now to the unit types you start with.
