There was an Audio Asylum member and speaker builder who built a subwoofer using a Home Depot plastic bucket (NO kidding!) and a Parts Express driver. According to all who heard it, it was pretty darn good. The build was easy to do and the cost was very nominal, less than $100. I think this is a the way I'd go if I were you.
Here is the link:
http://thehornshoppeforum.com/index.php?topic=406.0
-RW-
Here is the link:
http://thehornshoppeforum.com/index.php?topic=406.0
-RW-