I make $0.33 per mile, so if I drive 100 miles I get paid $33.00 to burn about $5.00 worth of gas (assuming 48-ish mpg). With my old car, a Geo Metro, I was paid about $0.21 per mile. I would burn roughly the same amount of gas, but only get $21. The Metro, of course, had no payment.
The $12.00 daily difference in mileage ($33.00-$21.00) multiplied by the 20 days per month I work makes the payment on the car. This is the reason I bought the Mirage...I essentially wasn't going to have to pay for it. My employer was going to pay me EXTRA to drive it.
When this car has about 47,000 miles on it (probably mid-2016), I will have been compensated the full cost of the car...with interest (47,000 x 0.33), but minus fuel.
Everything else they pay me after that, and until the car quits, will be gravy. Mileage compensation declines with the age and value of the car, so eventually...say ten years or so...I will be back to getting $0.21 per mile. But that's a LOOOONG time.
When that happens, it will be time for a 2025 Mirage and I can start all over again!