Dunno much about pcs, but about harddrive - what is the speed of it, you should have 7200+ but 10k would be more optional. 8gb of ram is nice for current gaming requirements, but if you want to use this pc for longer time, then more would be better, however you can always buy more easily. Adaptor 600w, this is bit risky. The more the better, i would suggest 750, cuz overloading of electricity is a bitch. About the price. The price level of hardware/software is relatively same in EU/US, but there is nothing easier then google the cheapest one in your region. The differences are big. In my country there is an e-shop which is 10-20% more expensive, but does most of sales cuz advertisement.
PS: maybe you should have asked before you bought it