Nowhere near as old as the previous post, but I found this cool little old Audio Devices (Audiotape) branded head demagnetizer in a junk box @ WeirdStuff electronics surplus yesterday.
Shown with it's listing in my 1963 Allied Radio catalog, at that point it was $5.88. Can't say how long it had been in production by that point, but it looks old.
In the same listing a 2,500', 10.5" reel of their normal tape was $7.12
A bit more research found it as far back as '59, but not in my 1951 Radio Master catalog. At that point they were mostly selling cutting styli and lacquer discs, though there were listings for acetate and paper base tape.