From my experience you won't get charged GST in a shipped/mailed item if the landed cost, including postage/freight, is less than $1000. Not 100% guaranteed but buying dozens of products over the years, I have only paid GST on $1K and up. Except, that is, when it comes via UPS. They charge everything they can including additional freight from Sydney to Adelaide. I hate 'em.
Waiting to see what they charge me on the current package, TheSky6.
Charles