Check a few other shops. I got one quote at $48 a sheet, and another at $30. I would never go with $48, but $30 was doable, considering it was less than 3 plexis. I've gone through two plexis on one OH easily.
Others may vary, but this is how I view it. An observation hive is built for one thing, and one thing only: to observe bees, i.e. to watch them. I can't watch them if they build wax on the glass. I can't watch them if it's scratched up.