Originally Posted by bear123 /t/1524325/subwoofer-suggestion-with-m-k-150s#post_24532642
Here are the option I would recommend in your budget range. $700 is just below some of the much better offerings, and just above offerings a step or two down from those. Here are most of your best options:
Hsu VTF 2.4
This is assuming you want dual purpose home theater/music subs, and have the space for moderate sized ported subs.