Generally speaking, a 1943 P nickel is not rare since more than 270 million of them were produced. However, there are some rare double die versions of this coin that could be worth as much as $400 in good condition.
A double die coin is a coin that has a slight repetition of the characteristics of a coin. This is seen in the numbers or letters on the coin, and also may be visible in the outline of the graphic elements. One should not assume that a 1943 P nickel is automatically rare, but if the double die exists, the coin is rare.
Though the 1943 P nickels that aren't of the double die variety aren't worth nearly as much, owners of these coins still can fetch more than the face value of 5 cents. As of 2014, even a 1943 P nickel in poor condition is worth around $2. A 1943 P nickel that's in stellar condition could bring in as much as $16 from a collector.
If the silver from this coin were melted down, it would be worth roughly $1.12. This means that this coin is worth more in its original form than melted down, which isn't true for all coins.