I've always wanted to participate in this sort of campaign, so I'm eager to give someone else some help. You could check out FF5's website - they have some good material relating to fuel costs. I've run the numbers a couple of times, and it looks pretty good - larger planes cost more to fuel up, as do planes with Extended Range or Multiple Engines, while small planes, or ones with Inferior Range, cost less. If you want, you could check out my Pay rules in the home rules section - they haven't been playtested, but I spent a good amount of time tweaking them, so they should at least be a good starting point. They're set up so that a pilot should earn, on average, somewhere between 1 and 2 thousand dollars per mission. I ran the numbers a couple of times and this appears to be about how much it would take to fuel, arm and repair a medium-sized plane (lighter planes would cost less, and heavier planes would cost more). The idea being that pilots should earn enough to break even, with perhaps a few hundred left over that they could put away (to use to splurge on expensive ammo or rockets, or to put away to save for a new plane).
Another thing I've worked is rules for pilots to purchase more supplies than they need (since they won't always have access to a repair bay or armory). Basically, pilots can purchase ammo, rockets, fuel and repairs ahead of time, which are then stored for missions where they might not have a chance to purchase these supplies. Basically, ammo, rockets and fuel can be purchased and stored and used whenever the player wants. For repairs, players purchase a certain amount of spare parts, which they then draw out of to make repairs (so say, for example, a player bought $1,000 worth of spare parts. Their plane was damaged in a mission and required $350 worth of repairs. They take this much out of their spare parts (leaving $650), which they could continue to draw upon until they ran out of spare parts).
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"Is it heavy?" "Yes." "Then it's expensive - put 'em back." -Jurassic Park
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