You haven't failed in flying Dec/ Jan unless you have work commitments (or similar) - flights are still available at decent prices.
If you're looking at the major cities (Sydney Melbourne, Brisbane, Perth, Adelaide, Darwin, Hobart, etc) prices aren't going to vary too much. You'll find there are cheaper suburbs in each of them. Sydney is still by far the most expensive though. A catch is that groceries may be more expensive as transport come into factor in remote towns.
Some general tips for all of them though -
* The further from the city, the cheaper accomodation will be. Check out www.realestate.com.au or www.domain.com.au for various prices of rental properties.
* Some job search sites in Australia are:
www.seek.com.au
www.mycareer.com.au
* You can have a good time anywhere, what sort of activities where you looking at? Party towns will be more the major cities but you'll find cheap/free activities in a lot of towns around the country.
And some info about WA (inc. Perth) for you - there's much more than just the Heath Ledger connection!
http://www.westernaustralia.com/au/Pages/W..._Australia.aspx