Theres alots of car sales garages not far from the airport in Perth, you'll have no problem finding a car, that's where OH got his from, and it fine with 1 year garantie, (it's second hand) and if you go with cash you can normaly get it cheaper!!...... (better getting a car in Perth then Bunbury, they seem to be cheaper !)
Best off luck.
I arrived 2 months ago (in Bunbury) it's great for families.