Consider this:
V-power is about 1.50/L, $85 get you 57 L of petrol, then you drive 350km, equal to 16.2 L/100km, if you are in sydney, driving everyday in peak hour, that is not a bad number, consider in sydney peak hours, 10 KM need 45 minutes to drive.
Test on highways really make differents, if it is arount 10L/100km, or even 9L/100km, There is nothing wrong with your baby.
Just dame traffic and goverment.