OR
look on the CUSTOMS website, regarding imports.
GST on the declared value of the item, and the shipping. Don't try cheat them down, they'll rip you a new one if you're caught out.
No mentions of a free ride for anything, even stuff you already own. You are importing it.
Yes, I have imported a container of aero things I owned, GST on them, and the shipping. No duty - aircraft and parts are exempt.
PLUS all sorts of fees that side, and customs brokers fees, AQIS and more this side. It's an expensive business, but fun when you open the box (assuming it makes it here alive!)
DB Schenker (Melbourne) brings in various aircraft for Avalon Airshow. Any customs broker can assist, it doesn't matter to them what's in the box.