What are your requirements?
Do you want a beach, schools, shops?
If you want cheapest I'd say that rules out the major cities - I haven't lived there bar Sydney when I was young but apart from that, I have read various articles on how expensive they are. I think if you want to be in a big city - Adelaide may be the cheapest option (but still deer.)
If you don't want to live in a major city - the bush is your best option.