Does anyone know the value (if any) of 20+ year old National Geographic Magazines?

My parents ped away and I'm cleaning out their things. They had saved their old National Geographics from the entire years of 1984 and 1985-including the well known one with the Afgan girl with the piercing eyes. They are in pretty good condition. I don't want to throw them away if they are valuable. I could use the extra money if they are worth anything.