Have a look at the sticky threads, there is a cost of living thread. they say you should take about 6 months backup (minimum). on an average a months expense including rental etc for 2 is 3000A$ (for a median living-no luxury). I would say get atleast 20kA$, beyond that, sky is the limit. Luxury for some is necessity for others.
How long is a piece of string? There is no definitive answer since it depends on so many things such as lifestyle, where are you moving to, will you have a job when you get here, are you going to rent or buy... etc.
Have you read through the sticky posts at the top of this forum? The 'PLEASE READ....' sticky post has links for properties for rent / sale and that is going to be your biggest expense.
There is also the 'Cost of Living' thread which will give you an idea of everyday costs.