I use USPS to ship to Australia, and it is generally fairly high. Fedex and UPS have always quoted me 300 plus sums, where USPS is roughly 150-200 depending on the size. Be aware that certain areas in AUS have size limits (because of the USPS counterparts there, not because of AUS, in general.) that with prohibit a full guitar+case in dimensions. I hate when that happens, because that means you are stuck with either UPS of FEDEX at the Captain Insano rates.
I've shipped about a half dozen guitars to AUS over the years, with 2 being within the last 12 months. It is never cheap or quick by any means.