Your question leaves some open assumptions which play into an estimate. Where are you, as shipping will cost more than the value. Are you buying it, are you an active player trying to sell it, or is this disposition of an inheritance/family issue.
These instruments are from 50 to 65 years old. Whether they had annual proper oiling, were played regularly, had the capacitors replaced, all factor into the value. Improper oiling or the instrument just sitting for 20-30 years greatly reduce what is already a very small value. I found an M-3 in perfectly good condition in a populated middle class suburb of Chicago at the curb about to go to the garbage.
While these are probably the loveliest spinets of that era, and fully restoreable by a dedicated player, they are only worth $50-$250 depending on location and condition, more hidden than apparent. Many ask much much more on craigslist and Ebay, but anyone can ask whatever they want. Few if any get it.