It's what we call an "Oiler". It is an early Nelson Paint "Splotchmarker", designed to mark trees and cattle.
You also have the original holster.
You may find a manufacture date under the grip panels if you look.
My guess? Late 70's.
As for value? $200.00.
He gripped the wheel, his knuckles went white with desire, the wheels of his Mustang exploded on the highway like a slug from a forty five. True death, four-hundred horsepower of maximum performance piercing the night, this is Black Sunshine...