Value is hard to determine. Maybe some of the members who having been watching ebay closer then I will have a better idea but I would guess anywhere from $6-$20 depending on how many bidders fight over it.
It could go higher if you have a bidding war.
The wrench that followed this one only had "Proto" on it but otherwise the same design. You have to give those away because fees would eat up any profit.
Regional value would vary but where I am you would be lucky to get $4 or 5 for it.
Cool wrench to keep for a reminder of your grandfather. That's how I started collecting a little Plomb a few years ago, trying to finish some sets my grandfather had.