You probably have a shop in town that sells acrylic sheet plastic. Haul the case in there, show them what you want to accomplish. Explain you probably don't want to spend a fortune on this. If they don't think you are going to waste their time they will sometimes be helpful, particularly if they think it is going to turn out to be something novel and cute. Ask for a little advice on how to cut and glue acrylic. You can buy a piece cut to size or you might even be able to get a small piece of scrap from their left over bin in deep red or even cobalt blue that should make an impressive front of a case if you illuminate it from behind with appropriate large LEDs.