Funny you should say this. I saw a great vintage machine on CL last night for $15 and thought it would be fun to buy a bunch in that price range that are working fine, and have younger women come into my home who want to learn to sew.
Food, fellowship and fabric. I would take a good look at each one and offer a smidge less. Sounds like he's just wanting to unload them, and if the grandmother had 4 machines, she enjoyed her craft and probably took better than usual care of her stuff.