One that we've used is near the bottom of the home page at .........
http://www.auinfo.com/.
One thing to be aware of is that there are 'Oz' prices and then there's 'Sydney' prices! Now I'm not talking as an expert (we're moving across to Sydney area early next year, so are not even there yet!) but we've spent hours & hours looking into all sorts of cost related stuff and have deduced that Sydney (and outlying areas) are not exactly cheap.
Like many things though, if you shop around you get the good deals, so if the price comparison for example, a bottle of ketchup, was taken from their equivalent of M&S rather than Lidl, you're going to get quite a difference!
It's the house/land prices that worry me a little. I'm hoping that they are levelling off a bit now but maybe someone over in that neck of the woods could give an 'on the ground' opinion?!