You can get PCI-e video cards that will do 4 monitors.
You can get a PCI-e video card with 2 monitors, and add a second PCI card that will do 2 monitors, but generally PCI video cards are overpriced and have terrible performance.
You say they're for business use. Will they be doing graphics work or anything, or basically just 4 monitors for strictly 2D use?http://www.newegg.com/Product/Product.aspx?Item=N82E16814195086
Will do basic 2D work just fine, and supports up to 1920x1200 with 4 monitors.http://www.newegg.com/Product/Product.aspx?Item=N82E16814133258&cm_re=NVS_420-_-14-133-258-_-Product
Same thing, from Nvidia, but supports up to 2560x1600 per monitor. http://www.newegg.com/Product/Product.aspx?Item=N82E16814139055
Dual 3450's on one card, 2048x1536 per monitor, quad DVI. Consumer grade.....