100-500 USD.
Is it possible you mean an AR 15 made with an elcectroless nickel finish?
You will have to call Colt
100-1000 or so
In 1974.
100-2000 USD
Made in 1976.
100-1000 USD or more depending on specifics
It was made in 1977.
1977.
If it's Colt, it'll be small hole.
Don't know value, but made in 1966.