Build your own if you feel up to it.  I recently did it and had fun.  This site is very good at helping you get the best performance for the $:   
http://www.logicalincrements.com/  The site includes build recs and also info on how they perform for different games.
I suggest starting with what performance level you expect.  For example AH does not require as much horsepower as some other games.  Here's the build I did for $600 and using parts from my previous machine:  
http://bbs.hitechcreations.com/smf/index.php/topic,382567.0.htmlIt runs AH3 with graphics on full, generally at 60fps (my 1680 by 1050 monitor limits frame rate to 60).  The one thing I am adding is new motherboard controlled fans, but I don't think they're necessary.  I also have a new 1440p monitor arriving tomorrow so I'll see how this build handles the increased graphics workload.
I also suggest taking your time and enjoying the process!  Good Luck!   
