I've shipped a car from Adelaide to Brisbane. The biggest thing is whether it's driveable!
If they can drive it around, it's much, much cheaper than if it's not a runner.
I was told that to transport it from Adelaide to Brisbane, it gets moved around 8 times - onto the local truck, off the local truck onto the first intercity truck, then most transport companies going Adelaide-Brisbane change trucks in Melbourne, then another change of trucks in the destination city, to get it onto the local carrier's truck, then off the truck at your place.
So it not only needs to run, it almost needs to be fully roadworthy - seats bolted in (mine weren't), reliable brakes, engine fires easily (mine didn't fire that easily), etc. And they won't let you have anything other than the spare in the car.
The cheapest I found were Moving Cars. They've had some bad press lately, and they did charge me three times (although it was a glitch, and I received a refund on the two extra times), but I got my gear. They subcontract it out (I think mine was done by Patrick or someone like that). They'll give you a price online pretty quickly.
And there were a few companies I rang in Adelaide who were similar prices - not quite as cheap, but close. I was told $480 from Melbourne to Brisbane, too, but the truck changeover caused by coming from Adelaide put the end price up... To about $900. And the size of the car doesn't get you a discount...
I got the impression that Adelaide to Brisbane and vice versa isn't a common route, either, contributing to the cost difference to Melbourne.
