Originally Posted by William
....so how is buying 2 projectors and a silver screen a less expensive option than glasses?
Depends how many glasses you buy...
3dxl x 2 = $800
hd66 x 2 = $1200
Da-Lite 8x10 silver screen = $600
hdmi splitter, filters, etc = $400
Total (without glasses): $3000
Single setup: approx. $1000 without glasses.
Active shutter glasses = average $100/pair
Prices approximate, of course, but if you're planning on buying more than about 20 pairs it is immediately cost-effective. If you don't want the headache or worry of batteries, failure, etc., then the passive glasses become more appealing.
The other consideration is that a passive system does not require a 3d projector, so if you're set on a 1080 display or special features unique to a particular projector, the dual setup potentially brings a very nice setup into the affordable range.
And, as mkoss mentioned, using a single projector and polarity rotator can trim ~$1000 off the price.