@pf2.0nyc:
The problem with the older stuff is it's SATA 1 or 2 at best and the power consumption is crazy.
I go in on drives with a friend and we buy in BULK so my price is closer to $100 per drive… maybe a slight bit more but we buy a lot of these drives.
That's my real challenge, it needs to be SATA2 or ideally 3 so the older stuff is out. <$400 is a goal... <$500 is not terrible... You know how these things go, set a target price and before long you are at $1000 a box. I just need something cheap and easy.
The HP DC7700's are SATA 2. Also, being Core 2 Duo, their power consumption is pretty decent, actually, probably about 60 watts at 10-40% cpu with 2 standard hard drives.
For new stuff, maybe look at cheap Home Theater PC setups:
http://www.newegg.com/Product/Product.aspx?Item=N82E16856115047
"Mini" system with full height PCI Express for $165 (after shipping)
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116410
Celeron G440 for $40 (free shipping, also you can go to Dual Core Celeron for $10 more)
http://www.newegg.com/Product/Product.aspx?Item=N82E16820313102
4GB DDR3 for $22 (more free shipping, double it if you want 8GB, it's got 4 slots.)
$230 after shipping for the bulk machine, if hard drives are $100 each, that's $430 total.