What is the value of us wartime silver nickels in plastic case?

Most of the value is in the coins rather than the case. The coins were put in the case by someone outside of the Mint, either a collector or a dealer, for display and/or sale.

Despite their interesting history "war nickels" in average condition aren't rare or especially valuable. As of 12/2009 their silver content makes them worth anywhere from $1 in very worn condition to $3-$5 if almost like new.

Uncirculated ones are worth more but you have to know the mint mark letter on the back to determine a specific value.