Aslan....
I would suggest a google search for car hire firms in Australia.
Then simply email them and see what response you get and what discount they are prepared to offer..
If you don't mind driving a campervan or motorhome and want to do some sightseeing this is one way with the firm looking for people to relocate their vehicles to their original base.The prices are veryyyyyy low but the trick is time and KM's.
Rental Relocations Australia New Zealand United States Canada - Hire Now at StandByCars
Cheers and best of luck with your holidays.