Ah, I misunderstood. Yes, you are correct. I would use the US government's rate per mile, which comes out to about $17 for 30 miles. Unknown what components this is expected to include beyond fuel and wear/tear.
EDIT: Found further clarification. "The TDY mileage rates consider the fixed and variable costs to operate a car (gasoline, insurance, wear and tear, etc.) and are intended to reimburse the average expense of using a POC for the official government travel."
http://www.gsa.gov/portal/content/100715
EDIT: Found further clarification. "The TDY mileage rates consider the fixed and variable costs to operate a car (gasoline, insurance, wear and tear, etc.) and are intended to reimburse the average expense of using a POC for the official government travel."
http://www.defensetravel.dod.mil/site/faqmileage.cfm