Prebuilt high end machines, especially branded ones, are usually a big rip off... like alienware.
The best way to buy a high end machine (if you REALLY can't just configure one yourself) is to buy a custom made one off eBay. I sold a few and actually didn't rip people off. Charged them what it cost me in parts + 50.00 for my time, and when I did that it was hard to be competitive. So there are good deals there.