I'm not sure if what you call "Plexiglas" is the same as what we call "acrylic" but I have made a screen from 6mm thick black acrylic. Having done this I would probably use 4mm acrylic if I made another.
Here's how I made it, started with a square sheet aprox the same size as the std screen that would fit in the oven on an angle, I made mine a little wider the the original.
Removed the std screen, placed it on the bench edges down but elevated on a block of wood.
Add a few layers of newspaper on top to protect it from the heat.
Remove the adhesive protecting paper from the acrylic and pre heat the oven to 170 degrees Celsius. Place the acrylic into the oven for 10 minutes or until it has reached 170 degrees. It will be flexible like a sheet of rubber at this temperature so be careful handling it.
Remove it and place it on the original screen, this will mold it to the correct shape. Once cool it will retain the curve from the original screen.
I then stuck the protective paper sheet back on the acrylic and used the original screen for a template to mark the holes and shape.
Cut the screen with a fine tooth jigsaw, be patient and work slowly. Select two drill bits, one small for a pilot hole and one the correct size. Blunt both on the grinder so the edge is not undercut, this will prevent the drill from biting into the soft acrylic and cracking it.
I used an orbital sander on the edges and finished off with some fine wet and dry paper.
All this cost me $40 and two hours work. An no more buffeting
I'll take some pics and post them this weekend