Build it yourself. That's how you'd get the best bang for the buck. PCPartpicker has a nice builder app for planning your rig:
http://pcpartpicker.com/parts/partlist/. Make a compilation and send it here for evaluation before buying anything.
The second best alternative is to find a reliable local builder shop to tailor the best compilation for you and then build it for a nominal cost. Of course you can use the tool above, get our comments and take the list to the builder shop.
The third cost effective way may be to get a cheap ready built and add what's needed for gaming. Remember, though, that with a ready built you really can't tell about the quality of the components used. Most often they're made to be used as is and adding a gaming level video card will require changing the power supply, which may or may not be wired according the standards.
Yet one point: If you can play AH with your current rig without problems, don't haste with the upgrade. No one really knows what the upcoming update will require, not even the HTC folks! All that is known at the moment is that HiTech is using a mediocre rig for coading and testing, so presumably if your current rig can run high details at 60 FPS the update might well be playable with it.
