Just purchased a new 5 speaker setup. Need 12" or 15" sub suggestions for <$400

[Big Daddy]

Do the following:

1. Buy a Dayton TIT320C-4 12" Titanic Mk III Subwoofer Driver for $160.
2. Buy a Dayton HPSA500 500W Subwoofer Amplifier for $250 or Bash 300W Digital Subwoofer Amplifier for $150.
3. Buy some fire resistant polyfill from Wal-Mart for less than $5.
4. Buy some 3/4" MDF wood from Home Depot or Lowes, cut them, and build a relatively large box. Alternatively, you can buy a ready-made subwoofer cabinet for less than $100.
5. Assemble the parts and build yourself a kick-ass subwoofer, better than what is available on the market.

If you decide to buy a ready-made subwoofer, you can buy an Elemental Designs ED-300 for $350 or you can buy an Acoustic Audio HD SUB12 for less than $200 or an Acoustic Audio HD-SUB15 for less than $270. For the AA subwoofers, make an offer on their Ebay store. You may be able to buy the HD-SUB12 for $160-$180. The above subwoofers go really low and perform much better than your current subwoofer.