I just did some quick computing here - let's say the average gas tank is 20 gallons on a truck/SUV. At $3.00/gallon = $60.
If you go through a tank a week, that's $60 x 52 = $3,152/year.
The girls are in their early 20s, let's say each has 50 driving yrs left. We'll add dad too, cuz maybe...