Skip the supercube, not a great value subwoofer.
Rythmik,
Hsu,
Power Sound Audio are my first choices for anything under 1.5k. If you can spend more than 1.5k, check out
Seaton,
JTR, and
Funk. These subs will provide a much higher value than the usual retail brands like Deftech, Velodyne, JL Audio, etc.