As you can imagine given the size of our country your mileage is going to vary depending on where you are. For example Sydney is much more expensive than where I live, Adelaide.
Anyway, I'll try and help as much as I can with respect to South Australia, and its capital city Adelaide.
Adelaide is roughly located at the southern coast of central Australia.
Cost of living is quite cheap here, for example petrol despite it being at historically high prices, is about 95cents per litre in the local currency, or approximately 65-68 US cents.
Costs at camping grounds and caravan parks will depend on where you go, but can be either free, or as little as ten AUD for a camping pass in our national parks. Caravan parks and cabins tend to be in the 30-50 AUD range per night.
I'm a student living in Adelaide and I survive with rent (about 360 AUD per month) petrol about 80 a month, groceries about 150-250 a month and for things like laundary you can go to laundromats here and get a few loads done for about $10.
As far as insurances I don't really know :)
Melbourne, Sydney and Brisbane would be a fair way more expensive. But definitely if you're coming to Australia use Adelaide as a base to go to places like the Barossa Valley, the Flinders Ranges and the West Coast (Port Lincoln, Coffin Bay, Whalers Way) etc.
You'd be suprised at just how diverse the environment is here, and Adelaide provides a good base to see it all.
Anyway hope this helps, if you have any more specific questions I'd be happy to help.
