Recently retired professor of medical pharmacology with experience in neurobiochemistry, behavioral psychology, English composition, and basic mathematics. Houston, Galveston and Austin.

Details

Basically, I would charge less per hour as the number of hours agreed to. For example, 1-4 hrs. would cost $30/hour while 5-9 hours would be $25/hour and 10 hours or more would cost $20/hour.
I would not charge for driving 10 miles one-way (or less), but more than 10 miles would cost one dollar/mile.