i have a great app on my iphone that i use called "gas cubby" works awesome with purchase price, maintenance, fuel etc all taken into effect.
I would use it on my dump but the odometer doesnt work :/
I use it on my pickup. as an example, went to west virginia this past weekend with 3 of my buddies. googled it was 800 miles round trip, $.35/ mile from gas cubby, had the gas split before we left.