I just received a spherex 5.1 system offered by parts express for 100 (but no amp for the sub) or you could get special price of $40/pair of speakers.
Too bad this isn't offered commercially anymore (with the amplifier/decoder/remote) because it had a lot of technology/features and great reviews. So add a plate amp, or just get a "real" sub that can cross around 120hz, and you have something that should be pretty nice. I haven't got it up and running yet, but I will be this weekend and let you guys know if its any good. One hiccup kept me from getting it fully up and running last night, is that the speaker jacks are rca female plugs, so you have to fashion some connectors to your speaker wire. I cut up some cheapo freebie interconnects that you get with new cd/dvd players etc. It was tiny wire gauge but it worked to try out for a little bit on a sonic impact.
-Tony