It's worth between $10 to $15 used.
About $30
100-550 or so
100-400
A center point scope would probably be better for an airgun considering it would be the most cost effective. A leapers or red dot scope is nice for combat and tactical operations because the illuminated dot allows for quick sighting in high adrenaline situations. I am assuming you are target shooting or hunting small animals with the airgun which is why a center point scope would be a good choice because it tends to be slightly more accurate for a much cheaper price.
100-425 or so
$55,000
45 or so
300-600 USD depending on exact configuration and condition. The scope doesn't really add any value.
Unknown caliber. Contact Ruger
25-75 usd
There is modest collector interest in Mossberg rifles from that period. Value will depend on EXACT condition, and completeness (many had rear sights removed to add scope- replacing them is pricy.) Prices for very good, complete, range from about $125-200.
Which one?