Just picked up the cr1710nx from CompUSA. $405 with tax, 250 in rebates. So, final cost will be about $156, including shipping/postage/tax.
Socket 939 Sempron 3400+ (2 ghz, 128k cache, dual channel capable)
Asus motherboard (unknown make) with custom no-overclocking BIOS, 2 SATA 4 PATA channels
4 PC3200 slots, comes with 1 PC3200 256 meg stick, CL3, infineon.
PCIe slot (yay!)
Delta 250 watt PS
combo cdrw drive
ATI X200 IGP video, which is pretty comprable to an X300 and TC6200 (read: some new games will run in low res, low detail, low eyecandy, no FSAA)
XP home license
100G Maxtor SATA drive
So, to turn this into a gaming machine:
$50-ish -- Power supply. Although this one might be able to handle lower end video cards, 14 amps on the 12 volt rail looks good.
$55 -- 1G of ram.
$120 -- 6600GT. I'm hoping for another sub-$100 X800 or 6600GT deal, or some other cheap alternative.
So when the dust settles, watching sales and hot deals can resulted in about a $325-375 gaming machine capable of playing new games, at least at low settings and low res.
I happen to have a bunch of PC3200 sticks lying around which were bought FAR or cheap after rebate years ago, and a few spare PS by Antec and Sparkle. So my cost for this box after the dust settles will be below $300.