One video card will work for 5 copies of wow, needs to be beefy tho.
What setup are you currently running?

At home I have a 22" and a 24" connected to the one graphics card.
My main displays on the 24", while the slaves are "maximised" into 4 sectors on the 22". Effectively the 4 wows are arranged 2 along the top, 2 on the bottom, each has the same amount of space on the monitor.