To add to Mayhem's post, there are loads of online websites where you can also get actual cost of things.
For e.g, one good way to find out the cost of food, is to log on to Woolworths or Coles online shopping websites. In the suburbs, prices will typically be lower but these websites will give you an idea of how much you will need to spend to keep your family fed. Once you arrive, shop around and after a while, you will know where to find the cheapest prices.
With regards to accommodation, have a look at Real Estate website. It's impossible to tell you how much accommodation will cost as the cost varies depending on location, size and age of the property, etc and a lot of these factors such as location and size of the property will be dictated by your individual needs.
There are also loads of helpful threads on the forum which answer your questions. A lot of them will contain links to helpful websites - I had a notebook in which I noted down any piece of useful information that I came across before I move to Oz. I would strongly recommend that you keep one - it makes life a lot easier when you're looking for specific information - saves you hours of googling. Or, alternatively, if you come across a helpful website, save it in your favourites as a few months down the line, it's often impossible to remember all these little gems that you came across on the internet.