Maybe 10 years ago I got a Luxman R-1070 for about $20-25 -- the glass had a crack, one FM channel was out, and the contacts were severely corroded. But I don't need FM, and after a heavy duty DeOxit treatment, works great . . . I use it every day.
Last year at a garage sale, I found a California Audio Labs Genesis CD player for $5. Works perfectly, in nearly mint condition. I'm sure they had no idea what it was; I was thinking it probably originally retailed for about $1000, but it was turned out it was more like $2000 in 1991.
About 2 months ago, found a Nakamichi BX-150 for $20 -- works perfectly, excellent condition.
Over 20 years ago, found a pair of Altec Madera 892a speakers -- cabinets very rough condition, and I had to replace the horn tweeters, but they were only $15. I also use them practically every day in a second system. But that's going waaay back . . .