Prior to checking out, when you click "my Cart" you will then see a button "Calculate Shipping". when I do that and select postcode 2000 I get the following FIMS price of $18 (that is a coincidence it matches the US$18 you wrote of). Don't check that option for USPS priority mail as FIMS has nothing to do with USPS, it is FedEx plus Australia Post.
Originally Posted by NDP_2010
Freestyle FIMS option example.png