Ok, He said AUS, as in Aussie, as in Australian Dollars(AUD).
Yes, you can pick up a 5770 for that price range and it should be quite more powerful compared to the EN8400GS Card.
Here's a link to pricespy.com.au, It has the cheapest 5770 at $200, I would however like to know your full system specifications.http://pricespy.com.au/pno_16925.html
theres the link to all the 5770's from cheapest to most expensive, I cannot comment on the stores seeing as I'm not Australian however.
Kiwis are better than aussies