Amazon has 500GB Samsung 850 EVO 2.5" SATA III Solid State Drive SSD (MZ-75E500B/AM) on sale for US$199.99
Its AUD $266 + ~AUD$8.00 for shipping. = $273.55
I think its the cheapest i have seen for this specific drive.
You can choose which one to go for either Samsung or Crucial MX100 512gb SATA III ssd (same price)