Depends on quite a few factors.
If it were brand new (still in boxes) I would pay $150 for the subs and box, wouldn't touch the amp.
All together, installed (with amp), no power cables and like new condition (less than a weeks use) then $100.
Used (more than a week), regardless of cables or appearance, no more than $50.
**The 600 watts refered to by Sony is 600 watts peak, which is basicly an imaginary number. You are acutally looking at closer to 200w rms power from that amp.