it costs much more here because there are no big manufacturers here in australia, everything has to be shipped there fore adding to the costs. i compared the system that i bought from australia costed me about $1600 and another system from new egg. same thing but is 300-400 dollars cheaper.
and plus the US is a much bigger country and has more stores compared to australia who are constantly competing for the best price. (australia is much smaller and a lot of stores try to rip you off) hence, there are ups and downs to both sides.