What is the value of a 1957 S US silver certificate?

Please check again and post a new, separate question. There were only 3 series of 1957 $1 bills - plain, A, and B. The series letter if any is next to the date.

In any case most 1957 $1 silver certificates are only worth $1.25 to $2.00 in average condition, regardless of series letter.