Thats a diffeent matter then, why do you need a sub? You may be better of with some £100 pair of speakers. I was given a Gale Subwoofer which still sells for £50 at Richers, it was ok if you have it on mild settings just to add a little bit extra to the bass but I found more than anything it slowed things down.
The eltax subs are probably a bit better though, I think you can get these for around £60, buy some JPW 310i speakers or Eltax Monitor III's and you should have a half decent setup for £100.