It really depends on exactly what your looking for. Could range from competition to turning on your neighbors car alarm when you drive by to just simple quality sound. I recommend 1 10' or 12' inch woofer in what ever box that is specified for whatever particular brand you choose; JL AUDIO, KICKER, and ALPINE are all good choices for any sound system. The watts of your amp should be based on your subwoofer handling specifications. Check out a magazine called CRUTCHFIELD, they normally offer excellent sales and packaged deals at almost unbeatable prices; after ordering you just have to find someone to hook everything up who know's what thier doing. Otherwise find your local authorized dealer over the internet or yellowpages and chat with them based on what I told you here. With what I recommended that should be a plenty and you should'nt spend no more than $650 including installation and that's extreme.Don't forget about wiring but they should handle all of that.If you have any more questions email e.turner81@yahoo.com
p.s.NEVER go to a flea market or average joe to buy or set up your system. That could spell disaster.