i3-2120 $110
Asrock H77 Pro4/MVP $70
Patriot 2x4GB $30 AR
Seagate 500GB $55
XFX 7850 2GB $180 AR
Antec VP450 $36
CM Elite 330 $30 AR
= $511 AR
Disagree about your point regarding Sandy Bridge. The difference in cost reflects the difference in performance between SB and IB i3's.
The 500GB HDD may seem like a needless sacrifice for just $10, but strictly for a gaming PC, that's fine. If you really needed 1TB, I would just recommend paying up instead of making other sacrifices. Or wait for an even better deal on a PSU. Corsair CX430 V2 has been as low as $15 or so.