Seen these on roe a guy was talking bout 15s. Dont know the price..
http://www.ddaudio.com/dd/caraudio/woofers.asp?series=3500e
http://www.reaudio.com/specs.html#sp_mx
ive ran all my w6s in a ported box and they were loud and sounded good at the same time. But from doing the research im sure you will be happy with either.