At work today I was able to whip up what I think is a decent spreadsheet for budgeting a road trip. Essentially you type in anything in the green area and the blue area is automatic. It even will give you directions and figure out your distance/fuel costs if you type in the route with proper spelling.
The catch is it is in google docs (must sign up) and then click the "File--> copy" icon to make any changes. There is a seperate tab for americans. Let me know what you think? If it proves to be useless to most people, then I will take it down and just keep it for myself. (I think it is pretty nifty)