Since you brought up computer builds....
....not sure if any of my info/specs are of value to you in your build, but here's what I'm doing at this time.
I too am building a new DAW computer....well, not a total parts-for-parts build...more like taking an existing ready-made "base" computer system, and then adding to it the necessary components and setting it up for DAW use.
First...I have ZERO qualms about buying on eBay.
I can cherrypick decent used stuff, and not spend a lot of $$...so if it doesn't work out, I'm not out by much, and/or I can buy spare stuff/parts, and it's still spend less on all of it than single new items.
I needed to find a computer with a 3-PCI (not PCIe) slot MOBO since I still use Echo Layla24 converter boxes, and their cards are PCI, and I have three converters. Of course I also wanted some PCIe slots for the graphics and whatever.
Since that many PCI slots are hard to find in more current computers, I went back as far as had to, which wasn't too far.
I picked up lightly used Dell Precision T3400 with a Core 2 Extreme 3GHz quad core processor, and then I picked up a second T3400 to have for parts if needed. Got them both for $200.
I dropped 4 2GB sticks of RAM for a total of 8GB of RAM into my primary computer (I have another 8GB for the second one)....and I may at some point buy 4 sticks of 4GB each and bump the primary up to 16GB total, but 8GB will do fine for now.
These Precision T3400 computers come with 3 PCI slots, 2 PCI x16 slots and 1 PCIe x8 slot....which covers my needs for the 3 PCI cards and one PCIe for the graphics. I'm going to use the x8 PCIe for a Firewire card so I can have that plus the USB connections, and I still have one PCIe x16 for whatever comes up.
I picked up 4 WD VelociRaptor 10k RPM SATA2 Enterprise drives. I went with 300 GB drives, as I don't like having once massive storage drive. I'll run one for the OS, two for audio work and the fourth one for samples. Got all 4 drives brand new for total $216/shipped...I plan on getting a couple more as spares.
I may even drop one drive into the other T3400, install the OS and my basic DAW apps (I can install the DAW software on as many computers as I like...all I have to do is move the dongle from box to box to authenticate)...that way, if the other one has issues at any time, it would be easy to swap the audio/sample drives and get going on the second computer without a lot of down time....though I doubt I'll have that need.
I'm just looking to grab a couple of used dual DVI cards on eBay, and pick the one that works best on my setup...and that's it.
For about $500 I'll have a pretty decent DAW.
I'm currently running an older Precision 530 as my DAW. It has dual Xeon 2.8GHz processors, 4 GB RAM and I've been running XP 32 bit.
One reason for this current build is because I want to go with Win 7 64 bit, since I can boost the RAM, and because my DAW software (Samplitude ProX) has an upgrade version coming soon which will not run on XP...so it was the right time to make the move with a new box, and I'm still able to stick with my 3 Layla24 converters, which I like a lot and don't have a need to change.
This new build, like my current DAW and the one before that....are all single-purpose computers. I don't run them on any network, and they are purely DAW computers....nothing else. So I run them as lean & clean as I can get them, and that makes up a lot for the fact that they are not the most newest generation computers.