Rui, perhaps you have misread the plate on the amp and the 400W is the maximum AC draw rather than the output?
the 400w came from the "vintage audio link" that axiom has. The faceplate on my sub states 165watts.
You can buy subs of comparable quality for $250-350 brand-new very easily. Since yours is quite old and has a suspect amp, I think you'd be very lucky to get $100 for it even in excellent condition.
Are they actually of comparable "quality" or have comparable "specifications"?? I would think there's a huge difference between those.
$100 would be insane. it's worth much more than $100 IMO. I guess i'll just list it for $250 and see what happens.