When I saw the original post I thought it was a little steep. BUT! It's copies of five manuals that were put out by Natcam. At that $50 point it becomes a lot better value. I was in their last residential course in 1992 & we got the same books they're about 5X8" & pretty good for the $$$.
If you can take a look at Thomas Tomosy's books, they can also help.