To check on the price of food etc at supermarkets, have a look at:
http://www.homeshop.com.au/category.asp?
Although by shopping around you can get things cheaper :)
eg: Woolworths: Milk Whole 2L = Price $2.67
I get it for $1.79 at my local fruit and veg shop :)
Potatoes can vary between 99c per kilo to $4 p kilo, depending where you buy them, what brand and in what quantity.
Be aware that Australia isn't generally big on "ready made meals", and therefore the prices for these are much higher, due to lack of demand.