I mostly use Europcar, for the rates. That's been in Sydney, & well in advance, & they were cheaper & available compared to the others. Note - sometimes the rate is better when you check as a non-member than a member! And use Incognito in your browser. I've also happily used Economy Car Rentals in Aus & overseas. The different comparison & direct sites have different deals too - some unlimited km's, some without (usually remote locations where that gives them a huge profit). The other tip is to fiddle with the pickup & dropoff time combinations, as that can sometimes effect availability & rates. Last, with overpriced locations due to short supply, try renting a second hand car, or a commercial vehicle or a ute from a petrol station, or Bunnings!