From what I remember, the KC-40 styles sell in the $100-150 range on US eBay.
Usually you can check eBay for an idea of the value. I don't see many KC series right now, however.
A couple of KC-70v models have been listed recently. The KC-70v is a little better model than the KC-40v. One sold for $105. One didn't get any bids with a $165 starting bid.