Bump'n an ole topic, but anyway:
As for the different range-payload options: is it possible to first ceck whether the planned route is within range of the aircraft, and if so, that a maximum loadfactor is calculated (for easiness, this could be linear), and players can then establish the price in the normal way, without exceeding the maximum loadfactor. This would for example allow an intra-europe flight at maximum capacity for the AN225, and a EU-US flight at less-than-maximum capacity, because you need more range.