There are wide range of rental car options available either at the Cairns Airport or around the Cairns CBD (Central Business District)
These include but is not limited to the following:
The Cairns Airport website has an excellent guide to rental car options at the airport. CLICK HERE
A generalized search of "Car Rentals Cairns" will lead to many websites for browsing. Also remember that some specific rental car company websites can provide valuable options depending on your needs.