Fellow aussie here, prices on hardware are always extremely tough. Try and find something local so you can save on shipping, but PC Case Gear is probs your best bet for something nationwide. That's brand new though, and to be honest, I would have to agree with zoltan. Your best bet for that budget is second hand. If this were 2015-ish 500 dollars could get you far, even at 1080p and 60fps for most games, but now after everything the market has been through - RAM shortages, cryptocurrency GPU price rocketing etc - $500 is not gonna cut it brand new. Maybe you might be able to find something pre-built, if you're lucky, but try searching for second hand gear.