100-1500 USD or so
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.
The Colt AR-15 Carbine with the serial number SP 212104 was manufactured in 1991. Colt's serial number system indicates that the "SP" prefix corresponds to rifles produced during that year. For precise information, it is always advisable to consult Colt's official records or a firearms expert.
100-2000 USD
1977.
100-1000 USD or more depending on specifics
Made in 1976.
It was made in 1977.
If it's Colt, it'll be small hole.