You must call Colt with the serial number to find out.
@1964
Colt first introduced the AR-15 SP1 in 1964. This model was the civilian version of the military M16 rifle and marked the beginning of Colt's production of the AR-15 platform. The SP1 became popular for its lightweight design and modularity, setting the stage for the AR-15's evolution over the following decades.
1974
100-1500 usd
100-1200 USD or so
You will have to call Colt with the sn to find out.
value depends on overall condition
1000 USD
1970
Post 78 given the sn you provided
Proofhouse.com has sn data.
500-900 uSD