was going through my standard catalog of military firearms and came across two polish trainers i dont know about. they are a WZ-29 and a WZ-31. they are both valued at $2000 in mint condition in this book. what makes these things worth that much? what is the difference between the 29 and the 31? i know this book is only a guide and the prices they list are laughable at best, so what are they truly worth?