While you've been able to pick up 4TB drives from Hitachi and Western Digital for a little while now, they've been enterprise drives, meaning an enterprise price.
You wouldn't get much change out of AU$560, in fact. Western Digital's new Caviar Black 4TB drive is an attempt to make that price a heck of a lot more appealing. While we haven't received an official release yet, the 7200RPM, 64MB-cache drive appears to be going on Staticice for around AU$390 at the time of writing, coming in at roughly AU$0.10 per GB. Considering that you can pick up a 3TB drive for around AU$0.05 per GB, it's still a significant mark-up — but no doubt prices will drop over time, as they always do.