To be honest, I'd recommend putting in AT LEAST 850 in Australian Currency.
Newegg is a pretty good site, but I'm not sure where they cover shipping. I can throw together a 550 Dollar PC and tell ya if it's worth it.
Windows 8 works wonders with a touch screen moniter, but using a mouse is torture. Windows 7 is a must.
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http://pcpartpicker.com/p/6Xv3WZ
This is the best I could do, without an OS, case, or Network Card. Yet it's still past your range.
Sadly I'm not the best when "more for your money" is a factor. I go for the pretty parts.
Hopefully someone who's better can help.