Checked fuel burns. Approx. 2.5% additional fuel burn per hour for each additional pound carried.
Example = 10 hr flight. You'd burn 25% of the additional weight in fuel.
288L is approx. 90 gallons. Eight lbs per gallon = 720 lbs.
25% of 720 lbs = 180 lbs.
180 lbs x $0.45(approx. fuel cost per pound) = $81.