I have a year 2002 Ford Escape and I want to get new speakers, an amp, and a subwoofer, I have plenty of room in the back for an enclosed subwoofer but I don't know what sort of subwoofer I should get and what sort of amp, I don't know the least bit about car audio. I already have the Stereo. I just don't want to go to a specialty audio shop and get ripped off, Thanks for any help 