this is probably flat glass- flat glass is the easiest to manufacture and work with and the cheapest
contact a local auto glass shop- they can use your other window for an exact mirror-image template
in your shoes I would buy a sheet of acrylic* at home depot and use a rotozip, dremel or jigsaw to cut to size
I'd guess $50 and an hour
mounting into the rubber seal is easy using grease and string ( see youtube)
if the rubber seal needs replaced check steele rubber products, they have all shape/profiles of window seal, weather stripping etc
Mike
* considering my PW windows are always covered, I might consider something tinted or opaque
https://www.homedepot.com/p/OPTIX-18...C-21/202038050