Those are actually very common knives. The Marines adopted a version in the early 40s, and later, various models of this knife were built for, and used by all branches of the U.S. Military. They are still in production, and are still being used by the U.S. military. New ones start around $79, and depending on the specific model, up to approx. $200.
As with anything vintage, condition is everything. That particular piece would be considered "fair to poor".
What really hurts this particular knife is that it appears that someone has tried to apply some type of finish to the handle (just behind the guard, and possibly next to the butt cap). With any vintage knife, ANY attempt at restoration, drastically lowers the value.
Value is often times in the eye of the beholder, but since these are very common, and the condition isn't so good, you're probably looking at a value of $15-$25 for this particular knife.