Road trains need all the road and expect on-coming traffic to head for the hills. They have trouble deviating and will wipe out a car rather than endanger their entire load. There are a large number of car rental agencies, both local and international. Competition means a range of prices and short-term specials, the options are worth investigating. Recognise that while unlimited kilometre rates are common around the cities, country and remote driving can incur a higher flat rate plus a kilometre charge and don t forget insurance expenses.
Smaller companies are often cheaper and it is worth shopping around.
They can be accessed on the Internet. A valid driving licence is essential and applicants usually must be over 21. One-way rentals between major cities are available but not very economical. Note that smaller cars may be cheaper but are not as comfortable on a long journey. Restrictions may also apply with regard to crossing state boundaries and, depending on the type of car you rent, concerning driving on unsealed roads.