Mathew,

Can't help much with pricing, I see those old bobs high and low. One bit
of advise though - more than likely some of them are full of Mercury.
Some folks will recoil in horror but the knowledgeable ones will pay
your price for an old mercury filled plumb bob.

On a side note, my Dad used to tell me that part of he and his friends
routine for getting duded up for a Friday night on the town was to rub
mercury on all the silver coins in your pocket to shine them up. He
lived to 89 and was active to the end.

-JP