I have just booked a Hertz car at Cairns. The qantas staff rate was no cheaper than the NRMA or RACV rate.
When I wandered around the Hertz website and combined special deals with the car club rates I saved around $150 for a ten day rental over the Qantas staff rate. Avis & Budget, using the qantas staff rate, were so dear they didn't rate a consideration. However for other locations, eg, Gold Coast, Avis was cheaper. Go figure.....
Do a bit of research on their booking engines for the best rate.