Originally Posted by
bigvuth
Let's say I first rent a car at the Brisbane International Airport. If I take a roadtrip to Cairns and back, it's 2100 miles. First of all how much does this cost in terms of extra mileage for car rental? Second are there any agencies with unlimited mileage? Third how likely is this to change in let's say four to five years? That's when I want to visit since I will have sufficient funds.
It can be cheaper to rent off airport. At times cars rented from airports have an extra (airport) fee. Look at insurance cost & t&cs carefully. It is a lot different to USA. As all the post above terms & conditions can & do vary a lot.
There are the main chains Hertz, Avis, Budget, & Eurocar and then secondary car rental companies, like
https://www.redspot.com.au/. As above
https://www.vroomvroomvroom.com.au is a good starting point. But in 4 years time it may be/will be different.
Note that Australia is
large and roads can be 2 lane. Up north multi lane free ways are not that common.