The Behringer B2030P is in a league above the Ascend CBM-170, if you want to be fair.
In all seriousness, though, if you want the best for the dollars spent, the Behringer B2030 is unbeatable; it's measurements(
the ones primarily responsible for perceived sound qaulity as is understood by the current perceptual research) are simply superior to anything else suggested here so far. It's not the prettiest speaker(it has no grill), and it does not have a fancy name, but if raw performance for the $ is what counts - show me a unit that even matches it - much less exceeds it - for even $600 per pair. But wait -- the B2030P costs $130/pair. From the cost alone, I expect not many will take it seriously - I understand that feeling. I did not believe it was possible to engineer a speaker of this quality and sell it for that kind of cost either - until I measured a set....
One could buy a set of these and get a nice entry-level hi-fi subwoofer approximately in the budget listed by the OP.
-Chris