Drew V:

I was thinking of building a couple of
screens with 1/2" steel conduit and some cheap plastic sheets in
the middle, but I haven't found good plastic to use.

There is a type of plastic made for bathrooms that is white, cheap, comes
in 4x8 foot sheets and can be found in Home Depot or Lowes. You could
punch holes around the perimeter and hold it in place with a cord. You can
paint it with spray paint made for plastic, or maybe dye it.
--
Mac Cool