The other day had the chance to get my hands on some pvc samples which can be used as a projector screen.
Have you considered to use this type of material as a screen? The surface is perfect as it is but it can easily painted if you wish. First thing i did was to measure their neutrality. Impressive results!! (i will upload the graphs later). Took a sample of 3mm and one of 5mm. Well...they are really light too. The 5mm is more rigid and practically needs no framing.
1 square meter of 3mm board weights 1,3 kg. That means 3 kg for a 92'' screen.
1 square meter of 5mm board weights 2,12 kg. That means 4,90 kg for a 92'' screen.
The only ''problem'' i have encountered is that pvc is available only in one size fixed sheet (3,05 x 2,03 meters). The costs (in Greece) are 68,63 E (including tax) for the 3mm sheet and 114,21 E (including tax) for the 5mm sheet.