Peleus it's a subject that has been covered a few times from a UK aspect, try a search on "cheap flying" or "PFA" (UK Popular Flying Association). If the Oz CAA is like ours, you cannot receive payment of any kind (I think) other than sharing the direct costs amongst the passengers AND yourself (corrections here please if I'm wrong folks).
However, you don't have to rent forever. You can buy a cheap (3,000 GBP) Evans VP-1 or a FRED or similar single seater which is usually VW powered and thus cheap to run. Then you need only rent when you want to take a passenger up.
