8-Tracks have actually become sort-of collectible to certain people. Most people won't pay 5 cents for one, but you find the right people, and they'll pay several dollars and up. Some 8-Tracks, which are rare and have very good bands on them, can go for $20 and up. Only places like eBay give you enough of a customer base that you can find these people. Of course, like anywhere else, it depends on the day of the week, as sometimes you won't get anyone, or you'll get someone bidding on an item for only a dollar.
Nat "King" Cole is well liked by everyone. All you have to do is find a record and 8-Track lover, and he'll be sold.
Certain Elvis 78 rpm records sell for a lot anywhere you go. Glenn Miller, however, not everyone is so familiar with (sadly). A really hot tune, "The Lady's In Love With You," will sell like any other 78 rpm record at 75c to $3 in an antique or record shop, but put that record on eBay, and it'll sell for $15 or more. Of course the Elvis 78s (certain ones) can sell for a hundred or so. Too bad not everyone is so enthusiastic about Glenn, but then, that makes the records cheaper for me.
Thomas