How much is it worth?

While this isn't really a technical question I'll try my best.
This particular model is a good example of a dual 10" sub with enclosure. I have seen these marked down as clearance (not this particular model) for $100 usually at these electronics stores when they are marked down like that they are sitting at about 40% of it's retail value. Used good tend to carry a value of about 25-50% of their normal retail value depending on condition age and demand. Car audio - at least around here - is not in as much demand as say 5 years ago, so I'd roughly estimate in a private sale you could get about $75 for them. Realise of course that your market may be different.