As helpful as the previous post was, I'll try to add.....
Cost of living in Adelaide will depend on how far away you live from work/how much travelling you need to do. Petrol obviously is a high price everywhere, but it will affect you more in Australia as towns and neighbourhoods are subject to 'urban sprawl'. Public transport is definitely nothing like HK in terms of speed, reliability and cost - but it can be great, depending on your location.
Groceries in Australia are cheaper than say, City Super or similar, but obviously more expensive than a HK wet market. There are also lots of fresh markets, farmer's markets and the standard of the supermarkets in general are really good. The quality of the local meat, seafood, fruit and veg is fantastic. Also mostly local, not brought in from all over the world like here in HK.
One note, Adelaide drinking water is known as some of the worst in Australia, so you will probably want to buy bottled water. (It's clean, just doesn't taste good)
Eating out is generally more expensive than HK, both low and high end. You certainly don't find many set price lunch or dinner deals, Super Monday's etc. Generally I find the 'Dining Out' experience much better in Australia in terms of service and food - you generally get more for your money.
Cable TV, mobile phone and broad band services are all more expensive in Australia. Wireless broad band is still unreliable in many areas.
If you are used to having a full time helper then the equivalent will cost you thousands of dollars more! But, if you have someone come in to clean the house once a week, it is actually very affordable.
When I say more expensive, I don't really think by a huge amount in general. For me, I haven't found living in HK much more or less expensive than Australia, once you take away rent expenses! The advantages of living in Australia is what you get for free - fresh, clean air, great beaches, landscapes, wide open spaces. Keep in mind if you are living in a house, you will need to factor in maintaining the garden/lawn - something not many in HK would consider!