Australian's should use US IP addresses to save money.
Choice, an Australian privacy group, has released a paper on how to avoid geo-blocking and price discrimination against Australians.
Their research has shown that prices, especially on IT purchases, are significantly higher for Australians than Americans, even before considering shipping costs.
Using a VPN based privacy service like Anonymizer Universal allows Australians (or anyone else) to use a US IP address to get the best prices.