You can get a universal if you so choose to, just make sure that it has the air space required for the sub that you choose. Now if you want a good sub at a low price, that will take some looking into; or you can look into this link:
http://www.edesignaudio.com/index.php?cPath=1_21
They also make really good amps as well. The subs pound like you would not believe. The low cost is only because you buy directly from the manufacturer, that and they come with a 5 year warranty and get kick a$$ customer service with this company. Everything you need to hook up a sub is this: amp wiring kit, sub, amp, and sub box. If you still have the stock stereo you will need a line level convertor for the amp for the sub, this is where the RCA cable from the amp will plug into. Other wise you plug the RCA wires into the sub pre amp out on the back of the stereo.
