That's a loaded question. The wb-2 is from 1942 and is the same as a Mercury kb1. I would think it would be worth a little more since it is an early model and was made during WWII just before wartime production shifted the factory to military products.
Condition is really the determining factor here. I paid $15 for my 1946 wd3 motor and have never paid over $75 for any of my Wizards of 6hp and less. Most folks won't pay more for a rarer year model although everyone would like to own an old one.
I would guess $250 would be the ceiling in my area and $150 would be more realistic for a running motor, but then There are no outboard swap meets within 200 miles of me.
Depending upon condition/completeness a fair price may be as little as $10 or if near original and the purchaser flush perhaps in $100-$200 range. Prewar Kiekhaefers are more or less collectable but they do not command a high price. There seem to be enough
of them around so that those who want one can usually
find one without much looking. Finding one complete
and in running or near running shape is a bit more of a challenge both to find and to afford. PreWW2 outboard makers and sales concentrated around
Great Lakes Region so finding an older outboard
not as unusual as say in Utah or South Carolina.