It was offered in the auction. It went for many, many times the flea market price. This should be considered a fluke. There are also instances where a key was way under bid. The value of an old key can be regional.
Older keys manufactured on the East coast are less common on the West coast.
Some keys made in the mid-West seem to be scarce elsewhere. The condition of a key is a primary factor in its desirability and therefore its worth. The only way to find the missing parts is to find an identical key. Depending on the scarcity of the key, you may never find another one. The value of an old key is whatever the seller is willing to take for the key and whatever the buyer is willing to pay for the key.