well a machine shop couldnt make them cheaper unless you did uber mass quantitys.  What I see there is a piece of extruded aluminum, c channel call it, then a flat bottom that would slide into the channel with a slot cut into it for the plexi, then you have the electronics and internal braces/ mounts. 
Now if you made them out of plastic, you'd have at least a 10k mold fee, but they would be super cheap after that.. soo if you want to make about 10-20k of them, I can get a mold made,, hehehe..