I have seen these and they look kinda cool. I think you have to paint them to match your interior unless you like the color it comes in. AFAIK, you have to screw them to the roof, etc. Don't they also have a place (console) to mount the stereo? It would keep things up and out of the way but might be too much work, especially for the wiring. IIRC, these are set up for 5" or 6" speakers which would be plenty for me.
Don't know about the price but $100 doesn't sound too bad if it's a new unit.
My $ .02
Rusty