Who would have thought that old microphones would be considered coveted collectors’ items? Musicians or producers are most likely to pay for them, so if you find out that’s who you’ll need to contact first.
You’ll also most likely find a microphone from a maker called Shure in your old boxes, which can sell for around $50. The rarest of finds, though, are the Neumann U-47 microphones from the 1940s which are worth tens of hundreds of dollars.
Perhaps if someone in your family used to be musically inclined you could be lucky to have inherited one from them!