I did not see a date on the ad. The ones from the 1940's to 1960's tend to be easier to find. Most of them go in the 20 to 40.00 range.
I have picked up several for my tool reference book collection. They can be useful, but sometimes it is hard to find the information you want. Also, you almost break your arm every time you pick one up.
The only ones I have seen go high at auctions are Buffum (early one with swastika logo), Keen Kutter, and Bluegrass.