I'm not sure what the IRS lets you credit for operating cost per mile for a vehicle used for business purposes, bu my former employer, the US government, as of a few years ago would reimburse us at the rate of $0.51 per mile. This was for the operating costs only, not including financing, depreciation, initial cost, etc. For a while, I was driving out to our lab in Ann Arbor, about a 500 mile trip, and would get reimbursed about $500 for the mileage (which included gas). But I did save on the cost of renting a car at the destination. Then I figured out I could just rent a car in Baltimore for about $200 plus gas (about $30-$50 at the time) for the usual trip. (That also saved me wear and tear on my personal car.) The contract airfare we had to use was about $400 round trip Baltimore or Washington to Detroit, plus, of course, having to rent a car to get to and drive around Ann Arbor. I was getting Roomettes on the Capitol Limited for about $400-$500 round trip, including the Ambus from Toldeo to Ann Arbor, though I did rent a car a couple of times at Toldeo.