Ring some other companies - that's a terrible quote.
I was thinking about this last night, expecting quotes to come in around the $1400 mark, it should be possible to get it back here for less. The flight has to be cheap (jetstar on sale), don't speed with it at ALL (lower speed = better fuel econ so stick to 110kmh and stay constant throttle not on boost off boost), drive each day until you're tired than put the seat back and sleep in the car (not as comfortable as a hotel but saves $80-100 per day and allows you to drive each day until you're tired so you don't rely on motel locations). It's not exactly a fun few days, but I've done similar (2400+ k's one go) and once you have a shower at the end and a good sleep you're fine.