If you are near the coast where there is a large repair yard, ask if they have a scrap pile of lexan and go see. If there is any that will fit your need, then it will be a lot cheaper as you will probably have to purchase an entire sheet which in the end the glass company would keep without telling you.
If you do cut, use slow speed with a blade designated for cutting metal. In other words, a fine tooth blade for lack of words. Also, remove the debri as you go along and take your time. Be sure to sand the edges. If you have to drill into it for screws, again go very slow and I would predrill a small hole to give you a point to drill with the larger bit but only put an indentation in with the smaller bit.
Never use acetone or anything like that when cleaning and suggest only alcohol. Hope this helps.