Affordable musically fast subwoofer


I am looking into acquiring an affordable and musically accurate subs, which will pick on the lower end notes of my Horn loaded single driver fullrange speakers. Besides those terrible 100+lbs subwoofers that retail 2-3k, is there something out there that is not necessarily hernia producing but that will actually be quick and musical enough for my horns?
The RELs are too expensive....decent used ones about1k+
The ACI Titan, seems to be decent, but still too heavy and moderatedly expensive at 1K+
The VBT Magellans, sophisticated, but the full set up, I wonder how good.
what about those mini SUNFIRE subs?
Any other ones that are easy to acquire in the used market?
bemopti123
Subs don't have to be "fast" (a bass note is quite slow in attack) they have to be "clean".

A lot depends on where you are crossing over. If you are crossing over at, say, 70hz or below the HSU VT3 is invisible and has great deep basss at around 800 bucks. If you are crossing over at a higher frequency I might rather go to a sealed box type. The Martin Logan ones are very nice (if pricy).

The trick is, the decay characteristics of the sub have to match the mains or it just doesn't gell. For instance, my speakers only sound integrated with ported subs; sensor-controled and sealed boxes just would not match no matter what I did. On the other hand my friends sealed box speaker sounded best with a sealed type sub.
I am currently using the NHT1259 subwoofer that I built myself, Madisound has the parts that are needed to build a low cost subwoofer, I like the sound of it for music, for home theatre? it could be better, but for the price I think that it is the best. The cabinet size may be a drawback, it takes a 3cu Ft enclosure. Check it out.