Check out this site that I found:
If you’re planning a mission trip, retreat or just a vacation you can use this site to calculate how much you’re going to spend in gas! You just enter in where you’re driving from to your location and what you’re driving.
For example: In November I’m going to Nashville, TN for the National Youth Workers Convention (yay!). If I drive my 2006 Jeep Wrangler, it will cost me $42.43 with the cost of gas at $3.70 a gallon.
Could you do all of this by hand? Of course! But why do all that work when this site takes less than 20 seconds?