Guessing installation will have a premium. Rain sensors tend to do that.$305 seems pretty reasonable to me. Lots of windshields today are 500-800. You can't really make one out of plexiglass for a street car, there are too many problems with that to describe here.
If this is for the windscreen at the rear of the cabin, reference price used should be the mopar windscreen: Here $439sorry posed in error thought this was about the wind deflector?!
If so see my post in What did you do to your Fiat 124 Spider today?
for $100 option