Quote from Scataphagos:
That's plenty. You should be able to get 4 x 24" for $1,200 or less, leaving $1300 for the computer.
ANY modern computer with at least 2, PCIEx16 slots will run 4 monitors on W7.
My choice would be a Dell Precision T3600 from their Outlet site. Don't concern yourself about "new"... Outlet computers come with same warranty as new. If you can be a bit patient, you can find almost exactly what you want for a good price. If I were buying one today and with some consideration to performance, I'd go for E5-1620 CPU, 4-8GB RAM, and 2x Nvidia Quadro NVS 310 or 315 video cards. Dell sometimes has their 24", 1920x1200 monitors for ~ $260 each.
HP will have a comparable workstation as the Dell but at several $Hundred more. (Both use OEM mobos made by Foxconn... might even be to the same spec.)
Thank you so much!