I had an AP 3k that I bought brand new for $270 shipped. It was on 2 800w rms Ascendant Audio Chaos subs that cost me $320 for the pair, and supplied power by 2 RPS industrial batteries that cost $100 for the pair.
For under $700, I could averge a 149.6-150.0 @ 37hz for about 3 minutes straight before the subs started to heat up at all. Must have put out good power (it would touch a 150 playing music, no wall) and was probably pretty clean if it could give the subs double their rms rating for 3 minutes straight.