If you have a motherboard capable of three way SLI, grab 3 GTS 450's off of Ebay for 80$ each.
He's running a sign. One low power 4-DVI card is $89.99. Two of any two DVI output would work also, but the MB cost goes up to get SLI or crossfire. Not sure why'd you'd spend $250 to $300 for three GTS450s to run a sign plus the money for a MB with three PCIe long slots, but you could.