oil change is prob better than flowers.
There is an exact formula for the mileage and it's been posted here regarding pass travel. the not-so-exact part if fees and taxes (domestically they are pretty steady--security, etc) then sales tax.

For INT, add the departure tax and EACH country's fees for tourism etc. That's where it gets FUN (not)

Have fun and travel safely! and NEVER EVER show up on my flights and outrank me!