Firstly, any route that takes enough time to prevent me from working in my home base town needs to pay at least $100 for each day that it keeps me away from home base. If it only keeps me away for 4 hours, then the minimum is $50 since I still have half a day remaining that I can work in my home base city.
I used to figure how many miles times mpg of my vehicle times price per gallon of gas times gallons of gas needed to make the trip, plus any add-ons for circumstances such as extra time and risk driving through rough terrain.
Then I changed to a $20/hourly number, which was surprisingly close to the same amount as the complicated formula above.
I currently figure my bids at $0.29/mile, which is $0.10/mile more than what it costs me to operate my vehicle (gas, insurance, tire wear, etc.) and is sufficient to allow for time spent. If the route requires more than one day, I add the cost of a motel. I also add for severe driving conditions.
It's not difficult or time consuming to know how many miles and hours your route will be. All it takes is a few copy and pastes of your shop addresses into Google Maps, and you will have miles and times and traffic. There is also software like MS Streets and Trips.
Sure, I would love to have $300 every time I drive 325 miles to Panaca to do a shop, but I think it builds better relationships in this business, and is more profitable in the long run to quote what you feel is your fairest price. I don't have time available to put my job schedule on hold while I negotiate job fees back-and-forth. I quote my minimum fair price the first time, job is either accepted or not accepted, and I can move on.