Amazon will only ship these to a US Address and according to users on Whirlpool you'll need to create a US based Xbox live account to use the card.
So you'll need to know someone in the US who can receive the card for you then email you the code..
Cheapest Australian Gold price I have found is ~$65
I would assume then if you play online and search for games "within your location", you will most probably play US players all the time. I don't like lag in my games so I'll stick to my Aussie account. If you don't care about lag then this is a good deal - you just need to make contact with your US penpal again :D