I feed 2 vehicles(Dad & Mom mobiles). These are in the "Bills" spreadsheet split to pay periods(1st/15th). Speadsheet auto-calculates $$$ per pay period based on vehicles mpgs, miles driven/half month, and the number keyed in for price of fuel. I ALWAYS KEEP THE FUEL PRICE ten cents HIGHER per gallon than actual to prevent "surprises"(i.e. Be prepared for oil company profit-harvests).
Example: my October 03 price was at $1.90. With our "overhead", a ten cent/gallon swing gives about a $10/month swing.
The other option(?) is to trade safety(big, heavy, vehicle) for economy(light, small, usually loser in accidents).