If you want to do it right (and you should, since it's for your work), you should really get two FireMV cards which are actually made for quad DVI. You could also get a Parhelia card, but those cost even more.
The FireMV 2400 is a great card which doesn't take up much space and supports quad DVI.
http://www.newegg.com/Product/Product.asp?Item=N82E16814102659
http://www.zipzoomfly.com/jsp/ProductDetail.jsp?ProductCode=321344
You only need two, then you can get just about any dual-DVI PCI-E x16 card you want, like a $90 Radeon X1300. You don't want to mix FireMV cards with GeForce cards. Last time I did that, installing the GeForce drivers seriously screwed up Windows.
I don't understand why you would need to save more money than that. If you can't spend $900 on video cards, how are you building a system with
ten 20" LCDs? It's totally unreasonable to spend $4000+ on LCDs and not be willing to spend $900 on the hardware to drive them.
That said, if you don't need room to expand, you won't be able to get much cheaper than getting four of the FireMV 2200s then one dual-DVI X1300. The cables would actually be a little easier to plug in on five separate cards.
The cheapest system I can imagine being practical for that type of thing would be:
CPU: Intel Pentium D 930 Retail
$178 (ZipZoomFly)
mainboard: MSI 945PL Neo-F
$83.66 (newegg)
video: ATI Radeon X1300 512MB
$99.45 (newegg)
video: ATI FireMV 2200 PCI
$139 (ZipZoomFly)
video: ATI FireMV 2200 PCI
$139 (ZipZoomFly)
video: ATI FireMV 2200 PCI
$139 (ZipZoomFly)
video: ATI FireMV 2200 PCI
$139 (ZipZoomFly)
HDD: Western Digital 250GB SATA WD2500KS
$83.99 (ZipZoomFly)
HDD: Western Digital 250GB SATA WD2500KS
$83.99 (ZipZoomFly)
RAM: G.Skill 2 x 1024MB DDR2 533
$143.98 (newegg)
CD: NEC ND-3550A black DVD-R
$35.99 (newegg)
case: Cooler Master Centurion 5 ATX
$64 (ZipZoomFly)
PSU: SeaSonic S12 500W
$129.99 (newegg)
I probably wouldn't want to go with a single-core setup. As far as dual-core, the Intel 805 runs a lot hotter, and doesn't perform very well unless you overclock it. Nothing wrong with going with AMD, but that'll be more expensive.
You don't seem to have a very firm grasp on the whole situation, though, so I'd be really careful about just going out and buying parts before you talk to someone who has done this kind of thing.