If I were putting them in my car, I would hard wire them to the back of the lighter or radio and then add a switch somewhere, and a fuse! (you might even be able to get away with taking power from the wiring for the power seats). That way you don't need a big 3 or 4 way adapter on the lighter and you don't have any wires running out in the open. That makes for a cleaner install and it would be much less noticeable, until you turn them on.
Around Seattle, I would check with Sound Advice, for most likely the best price. I know that Car-Toys will do it, or possibly Magnolia Hi-Fi. All of those places would do a good job and best of all they actually know what they are doing, although I sometimes wonder about Car-Toys.
