Car audio isn't what it used to be 10 years ago. Sure the Rockfords, Kickers, JL's etc. are still around but there is a new generation of companies that are putting out superior products for a much lower price.
Im talking about companies like Fi Audio, Sound Solutions Audio, Sundown Audio. Google any one of these companies and try to find something negative about them. Good luck with that. These guys are true car audio enthusiasts and with the internet they are making much higher quality products and selling them much cheaper by cutting out the middle man.
Whatever you do, please don't spend your hard earned money at best buy because they really don't no anything about car audio. You will be buying an over priced item built in China.
Fi Audio and Sound Solutions Audio products are made right here in the USA with skilled workers and at affordable prices. They also have excellent customer service.
DCON-10 D4 ? Sound Solutions Audio 10" 300W Dual 4-Ohm DCON Series Subwoofer
This is a sub that I would recommend to you. You cannot find a better subwoofer for that price, and I am not exaggerating. Not only will it pound but it has amazing sound quality, no Kicker, Rockford or anything at Best Buy could even come close to sounding that good. Designed and hand built in Las Vegas, Nevada by a skilled worker and for only $115, what else do you want?
Disclaimer: I am not affiliated with any of these companies, I am just a happy customer spreading the word and hopefully preventing someone from making a bad decision like shopping for car audio at Best Buy.