depedns on how you want to go... you can just get an amp and subs in a box and use a high to low converter and be done... most people will get a good headunit with xub out to the amp then the subs... you can go as cheap as you can find or as expensive as you can imagin...it is a personal preference... i would research diff subs and amps and headunits... and see how much you wanna spend and find something that you like.
Take out the rear seat and build a wall. Subs on the passenger side and port on the driver's side. Depending on equipment used, the projected cost would be anywhere from $500 up towards $10,000. Please be more specific with your question....
Street A dB Drag Racing
Have Termlab...will travel.