You need to call S&W with the serial number to find out.
The Smith and Wesson model 66-1 was made from 1977-1981.
Model 66 with the second engineering change applied
1980
50-400 usd
50-500 usd
Call S&W and they will tell you when it left the factory. The actual "build" date could be weeks or years before.
No such model in the S&W line.
1981
$450-$600, depending on barrel, condition.
early 80s
Check the butt under the grips.