I think this is the all-time low for this gigantic LEGO Technic set. Currently at US$329.99 (~A$445) at Zavvi US site with free shipping to Australia.
Cheaper than Zavvi UK or AU website which shows A$519.99 with free shipping to Australia.
I opted the US$8 method for shipping with tracking. Please note that this is a pre-order item with release date at 11/Dec/2020, so there could be a chance that it will not arrive in Australia until Jan 2021.