The diesel price is irrelevant to aircraft in Australia anyway... You use JetA1 !
I drive a BT50 3.2 litre 5 cylinder turbo diesel dual cab. I get sub 8 fuel economy on average and sub 7 on a long trip out of town, down to as low as 4.5 lp/100 coasting into the city at 80kmh down the freeway. You won't ever get that in a petrol equivalent with the power and torque of my diesel.
Diesel in Melbourne is within a few cents of petrol most of the time and was this week at 1.42.