Don't know about Australia but I have been shipping things to Germany recently and after checking with all the international outfits it turned out that the USPS was the cheapest by far. They will take packages up to 70 pounds. The cost varies depending on the weight and size of the package and there is a limit on the overall size of the package so you have to use those variables to calculate the actual cost. If what you are sending isn't too large or heavy they also offer what they call a large flat rate box that you can use for things that will fit in it and weigh 20 pounds or less.