The trigger guard was squared by welding and grinding, gunsmith work that never came out of the Colt factory.
Neither did the S&W rear sight in the "protected position" (Which is missing its guts, by the way.)
Nor did the rib on the slide, the beavertail, or the extended controls.
It isn't a Swenson.
Nor any other well known gunsmith I can spot by style.
I think it done by a minor shop based on gunzine centerfolds of the day.
I won't guess a dollar value, but if the gunsmith cannot be identified as somebody at the top of the field, it is not high.