As far as the value of his gun, it would depend on condition of the barrel and who made it.
For his idea of a sawed off home defensive weapon, a short chambered damascus hammer gun would be far from my first choice.
Find a used Remington 870 express or Mossberg 500 and trade him even up if you like the hammer gun. If he insists on a double go with a savage steven 511.
PS
http://www.shotgunworld.com/bbs/view...p?f=5&t=228535