I got to be friends with two company fleet managers over the years. One with a fleet of hundreds of our type of trucks, the other had several thousand in the US, along with a fleet of heavy duty trucks.
Initial cost, all costs of ownership (fuel, parts, oil, antifreeze, mechanic time and so on), then your exit price when you sell the vehicle. Pass it though Discounted Cash Flow Rate of Return (Internal ROR) and/or Net Present Value, and there you have it. They bought gas unless the usage mandated diesel (heavy loads).
Now for fun, I just loved towing for 10 years with a diesel, but don't confuse that with money. Fun and money, do not normally travel together.