[|Erasmus|]

Basically, you should be able to get something like this:

Antec Three Hundred Case $65.00
Intel Core i5 2400 $205.00
Powercolor Radeon HD6870 1GB $179.00
Gigabyte GA-Z68AP-D3 Motherboard $135.00
Antec Neo Eco 520C 520W Power Supply $69.00
G.Skill Ripjaws X F3-10666CL9D-8GB DDR3 $55.00
Seagate Barracuda 1TB ST31000524AS $109

Total $817

Those prices are from pccasegear, and they are not the cheapest of cheap places. Umart and Scorptech are good for Qld and should be comparable.

EDIT: IF you have a hard drive in your existing PC and don't desperately need more space, KarmaIT is right, it's a terrible time to buy HDDs. There is a shortage and they are overpriced. Better off not buying any hard drive then spending that hundred dollars on a SSD in a budget system though, either way. The $/MB is still very low on SSDs.