We've made numerous trips over the last 15 years and we have always hired a car from Rent-a-Dent, and will be doing so again when we are back for Christmas.
I used Naked Bus for some journeys whilst I was there earlier in the year, and if you book far enough in advance, you can get a seat for $1, though on some routes I found that 'advance' meant only a few days before. My daughter used Inter-city when she was over travelling to the Rugby World Cup matches, again booked in advance most of her seats were a $1.
Have a good trip.