I found a few boutique builders,
HardwiredPC -
JW Computers -
MWave -
OriginPC and possibly
CentreCom this one I'm not so sure about, I didn't get into the configurator so I don't know if it's simply a parts supply.
I'll suggest starting with those although be forewarned, some of those sites are quite fun to play in and it's quite possible you'll get lost (in a good way). See what you can configure for your budget then let us know, we can critique and tweak to (hopefully) improve value/performance