Today I was looking over some of the computer programs I wrote back in the 1980s when I had a Commodore 64, and suddenly remembered a very helpful book which I once owned. It was called "Mathematics On The Commodore 64" and I decided to see if there was a copy available online. There was - at Amazon - for $158 ! (I was expecting it to be about $20).
Actually I still have dozens of other Commodore 64 books in my library, and hundreds of C64 Magazines as well ... I'll have to see if I can get rid of some of them at $158 a throw.
I checked out some of the titles in my library and they are being sold at Amazon for anything from $2.15 to $99; most at about $18-$25.
On eBay the magazines are selling for about $5 each.