Onix X-Sub equivalent?

This might be a "sub" that is not going to turn any heads here at Audiogon, but I live in an apartment and was looking for a good, small, clean sub that would help fill in the bottom end of my Paradigm Mini Monitors. I'd decided, after reading a number of favorable reviews, to grab up an Onix X-Sub once they became available and I had the money. Apparently there were some available on 7/14, but I didn't have the money. Now I have some money, and they've discontinued the X-sub! So, I was wondering if anyone knows of an equivalent "sub" in terms of both price and performance. I was really looking forward to this box, which I heard mates with the Minis very well, and am somewhat crestfallen now.

Any suggestions would be greatly appreciated.