It comes from 1974.
A lot goes into value...condition, original box, papers, tools, etc. Does it have the original grips? Even the area of the country you are in can make a difference.
I don't see the long barrel very often but I would not call it rare and some don't care for the longer barrels.
With all that said if it is in excellent condition with no box or goodies I'd say
$500 to $600.
That is just my guess. I'm no expert.