That's very high.
You can get high quality .250" (1/4") thick 24x36 piece at Menards for $25 on sale, $32 regularily, and that would be enough to make the monitor bezel (24x24) and 1 large marquee (24x12). Now that isn't "Lexan" perse, it's the Lucite ES I believe.
Actually, around here, I can get a 22x32" piece of 1/4" TEMPERED glass with rounded corners and sanded round over edges for only $47 complete (e.g. a Ms.Pacman tabletop). It would be cheaper then for me to get a tempered glass monitor bezel (most likely to scratch and show), probably around $30, and then go with a cheap sheet of .1875 (3/8") plexiglass for $15 or so for my marquees instead of paying someone $75 for lucite.