We haven't done a great deal of travelling around, but most campsites we have been to seem to have rooms you can stay in, fairly basic, some are just wooden chalet-type but fine. We have done this when we have been with DD and SIL who have their own (very expensive) campervan.
Of course, you would still have to buy or hire a car.
Australia is very expensive for a lot of things these days, but the exchange rate is a bit better for us now than the last couple of years.
I have seen backpackers buying and selling vehicles at the side of the road! If they're sensible they would then take them to a nearby garage to be checked out.
I would be very careful if you buy one, distances are huge and if it should break down you could be miles from help. However, there are lots of 'Grey Nomads' on the road who would probably stop and help!