I would not want to use a lexan windscreen given the way that they get scratched easily and the poor visibility out of them.
My insurance covers a replacement windscreen once a year, which came in handy when it got a stone and the crack started propagating.
The factory replacement cost was about the same as mentioned above...
I found a non-OEM replacement that was ~300 and it works perfectly.
It was more the principle of wasting the extra $ that made me go for the non-OEM version... I would rather put the $300 one every year or two when it gets sand blasted or chipped, than have an OEM that is no better...
After all glass is glass.
Admittedly this is not in the US, but there might be a non-OEM one out there somewhere.