You can try NVIDIA Quadro NVS 440 not sure if you can play WOW on it though. If it can, then you can buy 2 of this and you have 8 monitors on 1 computer. No harm sending an email to Nvidia support to ask about it.

I have a old matrox MMS200 Quad series video card and it can't play WOW, it is good for 2D.