Hi,
I have never lived in Australia (yet have in several EU countries), and cost of living (as mentioned by others already in this thread) is linked to the local purchasing power (ie local wages).
a pizza in Oslo or Geneva costs a number of times the cost in Rome as the local salaries are very different. This can however vary for some products (alcohol or tobacco) were local taxes can make a big difference.
One consequence of this is that some people after retiring from high wage/high cost countries, then go to live in a much cheaper country for sun an more purchasing power.
Hope this helps,
J