The cable is $79.95 (US) + $2 for basic shipping (which is about $81AUD so say XE.com). If you want courier shipping it is $35-40 to Australia.
I checked with a few places and it is the same cable sold worldwide, here in Australia it seems to go for circa $175-200+delivery.
If you want to know more about the cable there are some details on the official site:
https://buy.garmin.com/shop/shop.do?pID=38354
In a few words it connects certain Garmin GPS units to the engine diagnostics system of cars with an OBD-II port.
More info on what it is, what it does and how to use it: http://www.youtube.com/watch?v=DFGsXfy2oR4
$80 is a good price for it as it usually retails for around $200 here in Oz.