The Australian dollar isn't what it used to be against its US counterpart, but even with the growing discrepancy, there are still bargains to be had overseas. Amazon tends to be the first place to visit for discount electronics and today is no exception, with the online retailer offering 5TB of external storage for less than $200, delivered.
Zirkaloy over at OzBargain has kindly run the numbers, and if you don't mind paying $16 for delivery, you can grab a 5TB, USB 3.0 Seagate drive for around $189, shipping included. Locally, the cheapest price I could find is $233 and that's without postage, so it's quite the deal if you're looking for some extra room.
As mentioned in the comments on OzBargain, you'll need a US-to-AUS power adaptor to use the drive.