If you want to save fuel and pay less fuel tax try this web site.
http://www.greenvehicleguide.gov.au/
The most economical are:
Toyota Prius
Fiat Punto 16 valve 90HP
Honda Civic Hybrid
Citroen C4 9HY
smart Cabrio fortwo
Peugeot XS HDI 307
Volkswagen Polo 3/5 Door
Volkswagen New Beetle TDI
Mitsubishi RG Colt LS
Honda Jazz Gli
But then there is depreciation.