I wonder if these could be mounted to the kick panels or the door's on our cars they are way cheaper than the kick panels.

http://www.lotusthermoforming.com/components.html

possibly, but youll have to use glass anyway so you might as well just fab up your own, im planning on replacing my door panels with some custom made ones from work but im gonna use a fiberglass mixture to mount some 6" speakers since my front polks are almost pure tweeter anyway, ive had multiple ideas like build an add on part that would just follow the carpet line on the lower part of the door etc, theres so much room to build out on the doors its not even funny, plus if you do your own setup you can angle them how you want instead of them firing into your leg