It depends if you want to go the cheap route or expensive route, when it comes to PA speakers most will go the cheap route when going with multiple speaker set ups (2 or 4 per or more per door). Now if you want to go the expensive route then you will probably just doing one speaker and tweeter per door. Its not that expensive but a single driver will and can cost you up from $100-200, depending on your needs/power and size. Brands include: Faital Pro, Whip Audio, EV, Selenium, Eminence, Soundstream, Hertz SV/ST Line, Audiopipe, Power Acoustik, Beyma, B&C, Crescendo just to name a few. www.usspeaker.com www.parts-express.com These are a few sites that I use to get my speakers and look at different brands and selections.