The value of the gun depends a lot on the condition. A Columbia Arms Shotgun ejector model could be anywhere from $100 to $1,800.
Value will seldom exceed 150 or so
The value of a 1905 model D single barrel choke bored Diamond Arms shotgun is actually dependent upon a number of things. Most importantly the condition of the shotgun.
I'd start at $200 and be prepared to come down.