I have a used one, been offered $1k for it. New in box should be worth much more, IMHO. Mine shoots great, accurate and functions fine. Advertise it and I'm sure someone will make you an offer you will like.
I'm not up on my flags, but isn't that a Mexican flag behind the eagle on the left side of the slide? Depending on who wants it will determine the price. For me, this would be a shooting gun, not a collectible. The pearl grips would go, and there would probably be some minor modifications like a spur hammer and beavertail safety. I love the .38 Super, and a stainless GM would be great to have, but not at a collector's price.
It depends how many Lew Horton ordered, I have one simular and he ordered only 30, but his normal order is from 250 to 500 units, since mine is a very low number I would not take less than $3500 and I also have a letter from Lew Horton stating that is was one of their units and the number they ordered.