My best bargains ever are a toss-up:
A) About 6 years ago I got a mixed lot of vintage foundations (garter belts and girdles) at a Goodwill for a buck or two apiece, some of them brand new and still tagged for sale. I still have them and wear them, all of them fit me well.
B) At another Goodwill I got a 60's vintage Nardis of Dallas Chinese red sheath evening dress with jacket in excellent condition for $5.00 and it looks fabulous on me. This is a prize collectible because Nardis was owned by Abraham Zapruder, who took the 8mm film of the Kennedy Assassination, and was known for working in his own frock factory.