Many Mobile Spa's charge a travel fee which is included in their cost of service. Some Mobile Spa's add an additional fee on top of their service fee's to cover travel expenses. How do you handle travel expenses when doing mobile services?
I would figure it into your overhead just like any other business. I figure how much gas I'll be using as a maximum based on the maximum distance I will travel and don't forget to compensate yourself for time. If you want to also figure in an amount for wear and tear on your vehicle that's another consideration.
Oh and I have a set service area. If your traveling extreme distances then you probably would want a seperate fee. If it were me I'd figure the cost of travel to the furthest distance your going to travel and go from there.