The value is and will always be however much someone is willing to pay for it, as is true for any object or intellectual/intangible property.
Your smith and Wesson model 686 is valued at 250-425 dollars depending on condition.
500-600 USD
300 or so
100-600 usd
Your Smith and Wesson model 19-3 which dates to the year 1975 will bring between 300-550 dollars depending on overall condition of the revolver,to include the amount of original blueing remaining on the barrel frame and cylinder,and the grips condition,and the barrel condition.
Try e-gunparts.com
Depending on condition; 0-500 USD.
Depending on condition 100-200 USD.
100-400 USD
Depending on condition the model 66 could be valued anywhere from $550-750.
100-200 USD
Depending on condition, $200-$350.