I have purchased vintage machines at reasonable prices at antique malls. I usually make an offer and the owners usually counter offer. Why not offer $40 explaining it needs rewiring before you can even see if it is fixable? If the counter is too high just decline. I ended up getting a nice Singer 101 in a #40 library table for $27 that way!
One thing I hate at antique malls is they often use the sewing machine cabinet to display other items (usually breakable items...) and you have to clean off the cabinet to even look at the machine! And then they put a sticker either on the bed of the machine or on the beautiful wood cabinet! Rant over. Good luck!