Value of this Spanish 20ga dbl

[Mulepadre]

Can anyone give me a rough idea of the value of this gun which was given to me as a gift?

http://www.smaria.org/Spanish.htm

Here are what facts I have:

Dbl Barrel 20 ga.
26" barrels,
3" chambers,
IC & Modified.
Derby (S.T.) Model [whatever that means]
It weighs approx. 6.75 lbs.

Made for American Arms, Inc.
North Kansa City, MO.

thanks,
Mike