MenuhinNo. Polycarb is not the same as the normal plastic that you might be used to. It's a thermoplastic that is a lot more durable, and for this purpose, has a lot better photo diffusing properties than plastic. It's actually not molded, but CNC'd into the shape you see.
https://en.wikipedia.org/wiki/Thermoplastic
If you look up the price for Polycarb from manufacturers, you'll also see that the price is very much in line with what they're charging.
http://www.eplastics.com/lexan_clear_polycarbonate_sheet