Hi,
At the moment, there isn't really a "guide" or price book for old tools, the way there is for Baseball cards, coins, stamps, beanie babies, etc. The hobby of collecting old tools isn't widespread enough for those, at least not yet (the one exception I know of is old planes, which I saw a published price guide on a few years ago).
I agree with Spongerich, you could probably find someone here at GJ to buy it for somewhere in the neighborhood of $15-$25. Some brands, such as Plomb, are more collectable than others here, for whatever reason, IMHO. If you had the same ratchet, but it was labeled "Blackhawk" instead of Plomb, I think it'd be worth less. Not because Plomb is better, but because there's more guys here that collect Plomb than Blackhawk.
FWIW.
Beerman