If you are looking to cut down on the dust in the air while sanding one option is to get a 20" box fan and attach a 20" x 20" air filter to the back of it.  That is what I use.  I got one of those air filters that is reusable.  I just blow the dust out of it with my air compressor.  It also has a thick plastic frame and I screwed right through that into the frame of the box fan to attach it.  It works well, but only in a localized area.  Being portable it is easy enought to move around to where ever you are sanding.