Plenty of woofers that will own a W7 and at half the price.
IDMAX probably one of the best out there, if you can get a hold of the older RE XXX,
i heard FI is making a sub that is superior to that of the W7, me personally im an SQ fan so i bought Soundsplinters RLP4 great SQ sub at a great price and can pound 500-1000 watts RMS all day long.
Another Sub that is probably the best sub in the world is the TC sounds
LMS-5400 Super Driver
its a superb subwoofer at the same price but
its said to be the best in the world, nothing will ever touch this sub.
Then you have the TC12oem something really special at a ridiculous low price look at its specs and you will see that price doesn't always mean quality and superiority.
http://www.tcsounds.com/index.htm