what are your top "audio bargins" in your system history?

The one and only NAD 3020A back in the 70's.  Was the start of you can get quality without all the fuss from NAD.

2 pieces I acquired on used market

A used McCormack DNA 1 amp cica 1995

Great piece that I intend to have upgraded at some point by the designer Steve McCormack 's company.

Also a used pair of Reference 3a L integre floor standers. I find my self listening to them more often than more expensive SSM 6 Salk Sound stand mounts which I bought new

Little Feat Time Loves a Hero test pressing with white label. 50 cents at a thrift store. I have over 2500 LPs and this is still the SQ champ. Runner-up is a set of Bowers & Wilkins DM 110i. $50 thrift store. These were cheap speakers to begin with so there's no way they should sound as good as they do. I think it has to do with the synergy I run them with Quicksilver and Prima Luna monoblocks

I was stationed in Germany where we could buy audio equipment at a substantial discount.  I bought a pair of Infinity RSIIb speakers that were simply superb.  Sadly, on a subsequent move in Germany—a decade later, they were destroyed when the  mover’s truck had a hole in the roof and they were soaked to the core.  I wanted another pair, but my lovely and very supportive of my audio addiction wife wanted something less dominating in the room, so I went for the Infinity Modulus satellite subwoofer system in 1992.  Just replaced them last year with Fyne F702s.

A Gustard R26 I paid full retail for ($1600) last year was the best bang for buck I've yet experienced in my system.