

The Walkman came out in 79 and was cheap enough for a present to a teen or young adult by 82, at the latest. Hell, if you wanted to raid your parents’ stuff, they may well have had a (mono) folio style cassette recorder or even a Sony TC-50 cassette recorder/player (which looks exactly* like a Walkman), made as early as 1968! They brought them to the Moon during the Apollo program. That’s right, cassettes technically came BEFORE 8-Tracks.
But they were too expensive until the late 70s, and by then most people already had an 8-track collection, so it took a few more years to mass adopt.
Source: I have mono demo tapes that my dad recorded from his poor Oklahoma farm town in 1970

My point wasn’t really about the price, but availability. You said you remembered Walkman as “way way later than the 70s” and I was just pointing out that, technically, they were kind of around the WHOLE 70s, just not priced or marketed in a way that they would have been very common, and hence why you remember them “way way later” (probably sometime around 82-84, right?)