2 years ago I had a want ad posted on CL and got some responses. Most replies were bogus or offered junk, but one guy did have a nice, small raw collection of 50s - 90s cards that he sold me for $225, which included a 69 Reggie Jackson RC, 59 Gibson RC, 59 Mantle AS, Clemente, Kaline, Wynn and Killebrew, 54 Ted Williams, 89 UD Griffey, 76 Eckersley and Ryan (and a bunch of NM commons), 82 Fleer Ripken, and a bunch more - all together worth maybe $500 - $600). I got several graded this year. The Reggie came back a 4.5 (looks EX/MT), the Mantle got a 5, the Clemente and Killebrew both got 4s, and the Gibson got a 1.5. I still need to get the Griffey graded. Looks Mint.
So, if you're willing to put the time in and put up with meeting a few people who claim to have vintage cards (won't send pics) and bring 1991 Conlons of HOFers when you meet, there's a chance to find good stuff