There is no automated shipping module for Australia post. Only for UPS and FEDEX, so I did get a quote at some time to have it implemented and it was over $1,000. This would be written and then added to the core product.
You would also need an account with access to the Australia Post API for automatic calculations which my clients did not have, so we did not proceed with this option.
you can email catalook directly on [email protected]
to quote for you.