Bear in mind that purchases over $1000- are taxable on import into Australia (you have to pay GST and any applicable import duty).
Prices are not always as simple as they seem - different countries have different tax structures, for example.
Also, you will not have any local warranty support in Australia with regard to the inks. Your printer will still be covered, of course, but if you have a problem with the ink you'll have to return it to the US.