I don't know if it's worth $50, depends on how much you want it. I took the National Camera courses in 1969-1971. They were very good. I found I could fix most any piece of photographic equipment from this education. Tom Love, the founder & president, was a neat guy. Met him an an AOPA Convention in San Antonio in 1975. Unfortunately, the whole thing went bust later.
I still have all my books, which are helpful for fixing old cameras. Nothing on the electronic cameras, however. They came later.