You can
build a pc, and load it up with cheap graphics cards. Radeon 5450 or other low end cards will work fine, and can be had for sometimes $5 each. They only need 1-pcie lane even though they are in a 16x form factor.
With 4 you can get 8
DVI/
HDMI or 8
VGA, or a combination of the two. ***EDIT***
Qlab is
Mac only isn't it?! Well this might be useful to someone else, but probably no useful for
Qlab.****
Black magic also makes an 8 out
sdi card, but most of these types don't have processing
power.
The maxtor tripple head togo do work, I have run, I think 9 or ten outputs with the combination of a few video cards and the trippleheads, from one
mac pro.
There are also options with programs like provideo player, you sync control of several different machines over the
network, from one master, I'm not sure if
Qlab offers that sort of control.