Bob, any glazier can work with any glazing. Glass, plexiglass, lexan, all get referred to as "glazing materials".
But all lexan is not the same, you will find at least a dozen grades of it just from GE (the trademark holder for that brand) alone. I would suggest that when you get estimates, get specific estimates for the exact material grade, color, and thickness that will be used. You may find a 10x difference between polycarbonates (i.e. Lexan) and acrylics (i.e. Plexiglass) and a 4x-6x difference within each material group as well.
A glazier usually will buy in full sheets (4'x8') and charge you per sheet--keeping the excess unless you ask for it. Hey, it's yours, it might be of use elsewhere on the boat. And that can make ordering replacements from a manufacturer cheaper, or competitive, since they aren't charging you for full sheets.
The proper bedding and sealing compounds can also be damned expensive, if you look them up they aren't your $10 silicone seals.
And, they are important. If you use the wrong sealant--you can craze the glazing.
All of the glazing materials come in different grades designed for UV and scratch resistance, and with a deck hatch you want the best resistance you can get. It is UV and petrochemical exposure that usually makes them craze.
Do you need Lexan? Possibly not. 1/2" or 5/8" thick plexi can take a lot of abuse, you'll need to decide that one yourself. Dropping a spinnaker pole from a mast mount into the hatch cover...you might want Lexan. going offshore and having green water drop 40' onto it, same thing. But many boaters don't want to pay 10x the price for the glazing to withstand that if they don't need it.
