car subwoofer installation?

downstat

I've done it before, with the same subwoofer in a different car, but the car I have now... well, I don't want to be pulling apart the interior on a city street. Plus the time. Anyways, does anyone know a good place / how much(?) to have someone install a BASIC powered subwoofer? All I need to have done is have wiring run through the car back to the trunk, to hook up to the subwoofer ports. Then splice open one rear speaker cord to the sub port. It's really easy, except for tearing apart the interior walls to get to the speaker.

Btw, its not a "set your car alarm off" type of subwoofer. Its a small 8" enclosed speaker. Just a simple way of adding more juice for my tastes. Thanks!