I purchased the Dazian Matte White PVC screen material off of their Ebay store, built my own DIY frame, stretched the material around the frame and attached with Velcro. Works for me for 100 bucks or so.
Some of the Ebay stuff is crap, so be careful.
It basically boils down to if you are a DIY person or not. Screensize has to do with your room size, seating distance, etc.. Heck, if you have a Menards, Home Depot, etc. some people buy the Parkland Durotherm Lite panels which come in 4' x 8' and can be trimmed to match your desired size.
The 900 has good contrast ratings, so I would not worry about getting a high contrast screen. Matte White (1.0 gain) or slightly higher will work. Heck, you can also such paint your wall with one of the many DIY methods discussed on AVSforum.
