I think of vintage as being pre-1972 when they started making the B-style 'harps with the top loading string anchors rather than the nails on the end like the old A-style 'harps with the square edges.
I own three A-styles from the mid-sixties, 2 Appalachians and one black box that I've converted to either semi-diatonic or diatonics and one old back box that I've left chromatic. I did a lot of work on all of these, but they are now great 'harps.
The most I paid was $30, but by the time you buy new strings and felts, you've sunk a lot more into them to get them playable.