film8ker said:
There was a mention of the Tiffen site, check out the Ultra Contrast filters. They may help.
If you are looking for monochromatic flat and lifeless, I'm not sure that you want to use the Ultra Contrast as it will tweak up the difference between blacks and greys. I can't actually see your vision, of course, but "flat and lifeless" suggests little contrast. I don't know much about your camera, but if it has internal neutral density filtration, use it. If not, ND screw on filters are pretty affordable. Another great filter (Tiffen) is the Black ProMist #1. You could add it to an ND filter and it will reduce contrast without blowing out the whites. It would also be very useful in your "real world" scenes as a stand-alone filter for it's diffusion/softening effects - makes your talent look good and adds a bit of the "film-look" quality everyone in DV is looking for. Once yo've got a ProMist, you'll use it over and over.
A Black ProMist and an ND filter (internal or external) together would reduce the amount of light reaching the camera's CCD, so you would have to open the iris to compensate, which in turn would reduce the DOF and further enhance the "film-look".
You could also go for the stuttery Private Ryan/Gladiator look in the highway of death world by overcranking the shutter. Could look really cool.
You could also try experimenting with gels (cheap) in front of your lights. Add some blue for an otherworldly effect. Try white balancing on something other than white - a yellow legal pad, for example. Just remember how you balanced so you can repeat it.
I hope I'm not being condescending.
Experiment.