What is the value of Saturday Evening Post covers?

The value depends on several factors. What the covers are about, when they were published, and the condition they are in. If a famous person is on the cover they could be worth more depending on the person and the reason why they are featured. There are books for info on this. Go to your local large bookstore and find the collector section and there should be a book there listing info about this. If not, take your magazines to a good bookstore or antique store and ask them, but be careful because sometimes they will under value an item so you will sell it to them.