the great gazoo!!

I've always wanted one of those, " I found this behind an old picture... " moments. Well, this last weekend, my mother provided me with one! A friend had given her some framed drawings and sketches and when she wanted to use the frame of one of said drawings, she gave us that moment.
Sitting on construction paper and accompanied with a signed letter from the secretary of Mr. Joe Barbera, was one animation cell of The Flintstones' " The Great Gazoo."
The letter states that TWO cels were gifted to a letter writer (apparently in regards to either the character merchandise or animation cels of him) in 1979.
My mother thought about throwing it out, but instead kept him in the frame that he has been hidden behind for over 30 years.
She isn't looking to sell the cel, but is interested in knowing if it's a mass reproduction or a one-of-a kind. If it has any monetary value, then that's a lovely bonus!