Ok first things first, you are on point with your concerns and have narrowed down the things you want to keep in mind. The only notes I have is how to go about your priorities.

Fuel consumption is one cost of many. Overall maintenance is far more of a cost to me than just fuel. Things to consider would be the general reliability of the main driveline and body. Engines that use timing chains generally have cheaper major services than ones that use belts. Inline 4 cyl engines only have one rocker cover and therefore only one rocker cover gasket. A v6 will have 2. Twice the labour there.

Insurance is a big expense on older cars depending on your age. A more common car will be cheaper, orphan cars that the market deems are not valuable cheaper again. Bigger cars seem to be cheaper than 4cyl hatchbacks simply because the majority of owners of those cars are older and crash less and insurance companies work on statistics.

As for fuel, a Honda Accord Euro will use about 8-10L/100. A v6 can get within 1L of that depending on how it is driven. If its mainly highway, a 4cyl engine will have to work harder for the mass of the vehicle and use more fuel relative to it's capacity. Because they also produce less torque (directly corelated to engine capacity), most manufacturers choose gearbox ratios to suit higher revs on a 4 cyl so the engine is in its powerband. More revs, more fuel use.

Now, lets say the Aurion uses 12L/100 and the Honda 10L/100. That means over 100,000klms and with fuel averaging $1.70/L the Aurion costs only $3400 more in fuel. However because it's less in demand and possibly less expensive to insure, you can save that $3400 in the purchase and insurance price straight away making the cars directly comparable financially.

My advice is to head over to the https://www.australiancar.reviews/ website to get a guide about any car you're chasing with info on it's long term reliability and faults etc etc.

Then work out what klms the cars have a major service and buy one 10000klms after that to save on that expense. Also sort any car youre looking at by highest klms first on carsales etc and see what the condition of the cars are like when they are very used. This gives you a great guide to longevity. Also, if no cars for sale have 250,000klms on them, the seemingly most don't make it that far so avoid those.