This is the best deal I've seen around. If you think about it, 640 GB for $85, that's equivalent to more than 7.5 GB per dollar.
The place is called MSY and it's well known for the cheapest computer parts as well as bad customer service. However, the money you save is worth it.
There are branches in Victoria, NSW, Queensland and SA. Refer to the website or price list for more details.
MSY publish a new PDF price list everyday so best to bookmark their direct link here: <br>
http://www.msy.com.au/Parts/PARTS.pdf