What is the value of a set of US wartime silver nickels?

The exact value would depend on the coins' dates, conditions, and mint marks but on average, "war nickels" retail for about $1.30 to $1.50 each as of 09/2014.

These special coins, minted from mid-1942 to the end of 1945, contain about 1.3 grams of silver with the rest being copper and manganese; nickel metal was needed for the war effort. War nickels are easily distinguished by the large mint mark above the dome of Monticello on the back, and by the fact that they were the only coins minted before 1979 that had a "P" mint mark for Philadelphia.

Various claims you may read online to the contrary, they're also the only US nickels that ever contained any silver. All other nickels made since 1866 are struck in an alloy of 25% nickel and 75% copper.