Credit to EggMan28 for their comment on the previous Woot deal for finding this cheaper and easier option. No need to use a forwarding service, can pay by PayPal and no GST!
The shipping estimator does not show Australia as a shipping destination. But as noted on the BuyDig shipping and returns page:
We currently ship to the following international countries: Canada, Great Britain, and Australia.
Shipping costs of US$40.99 are added in the checkout after entering address and payment information. This brings the total to US$429.99
The 256 GB version is also available for US$509.99 (about A$695) including shipping.
As noted in the other deal, although locked to AT&T they can be unlocked free by requesting an unlock code from Microsoft directly. Either by live chat, or calling their US support number +1 (800) 642-7676.
Is warranty affected?