Yea, electric power tools were not cheap in the early 40's,
A 'cheapo' economy 1/4 electric drill was $20, a good amount of money back then.
But the Electric hammer had the possability of paying for itself, think how long it would take 2 or three guys with star drills and sledgehammers to drill a few holes in a concrete slab, and how long it would take one guy with an electric hammer to do it. Thor also didn't have much competition in this area, the only other hammers listed are Black & Decker's, one cheaper, the other three are even more expensive. Their top if the line model is $195, tho it seems a bit heavier than the Thornado, and you also get a can of oil with it...
I suspect mostly companies and the railroads were buying these things, (the RR's were using them to notch railroad ties)