If you can't do a good estimate of fuel costs just make an arrangement with your buddy for him to pay your actual fuel costs, and leave town with a full tank (paid by you) and fill up when you get home, giving fuel receipts to your buddy to reimburse you. About 3 cents per mile covers the cost of oil changes and tires, which is only $18.00 for this trip.
For my friend I would do it for the cost of fuel and enjoy getting out and seeing the country. It should also be an easy 1-day trip if you leave early and the transaction and loading doesn't take very long. Oh, try to get a good snack and dinner budget out of your buddy, too!