I shipped a bike to Japan (also part of the pac rim) and used two 108 inch dimension BMX boxes and it was like $110 total for both. So I just went to the USPS on line calculator and chose Australia for a package weighing 30 lbs (far more than one of two boxes would weigh) and asked for rates. It came up as $52 surface rate for each box which sounds reasonable. Then I clicked on a link that would tell me dimension limits and as you say they limit it to 79 total length and girth. So then I went back and changed the country to Japan and used the same exact data and guess what the size limit changed to 108 total length and girth. Same as your average BMX box and still the price was a reasonable $51 each. From that I can only draw the conclusion that Australia must have a limitation on the size of package that can come into the country surface. I wonder if it would be cheaper to send through another country if you could have someone would would be willing to act as a transfer station.
Ray Homiski
Elizabeth, NJ