Seems pretty cheap, but would it sound decent?

http://www.bestbuy.ca/catalog/...20119

 

Yes cheap. But nothing will come close to that price. It looks like you will need another set of coaxial speakers(if you have 4 interior speakers), an amp for the subwoofer(use the included amp for the coaxial speakers), and all the wiring($50-100). The package is not as complete as they would like for you to believe. You don't have to have the extras I mention(except wiring), but it will sound better. You could buy 2 packages and sell the cd player and sub/box.

The best idea is to piece together quality components. You could start with these 3 : Subwoofer $150 shipped http://cgi.ebay.com/KICKER-S12...wItem
Amplifier $200 shipped http://cgi.ebay.com/NEW-KICKER...wItem
Box needs to be made to specs of the speaker. Have one built. $100. Have a friend build it if you know someone good with carpentry and can read the specs. off the kicker website $50. . About $400 total. still need cd player, coaxials, amp, and wiring. So, as you see this way the price ads up fast but has many advantages. Either way you will end up spending more than you think.