The problem with shipping to Australia is that you need to use
FedEx, UPS, or a similar service. The Postal Service will not
allow you to ship jewelry or metals there.
On another note, FedEx, UPS and other carriers who handle packages
from the U.S. to foreign destinations will charge a handling fee
(sometimes called a brokerage fee) to get that package through
customs. This comes on top of any duties paid. I think the cheapest
brokerage fees start at about $15.