I've never seen anything but junk at Goodwill and flea markets. The best deals have been via local Craigslist, where people who took good care of their gear just wanted to get rid of it for a nominal price. Of course, there is some junk you have to sort through. 2008-2009 seemed to be when the best stuff was available, when people were finally transitioning to digital.
Some examples:
Minolta XD-11, MD Rokkor-X 50mm f1.7 lens, Vivitar 283 flash for $30
Minolta SRT 201, MC Rokkor 35mm f1.8 lens, Vivitar 252 flash for $40
Olympus OM-1, Zuiko 50mm f1.8 and 75-150mm f4 lenses for $30
Zeiss Ikon Contaflex Super BC with lens shade, Ikoblitz flash, case and bag, and assorted lens filters for $25
All in like-new condition and new condition after I had the Minoltas and Olympus CLA'd.
Same situation with darkroom equipment.