Setup an account with a company like Shipito and get the item shipped to them (your new US mail address) when it arrives they will provide a whole heap of postage options to forward it to you in Australia. They add $2 on to the postage costs.
This will likely work out cheaper for you if you use the cheapest option which is airmail.
Anyway multiple options out there to buy from the US and avoid getting stung by the high postage charges.