In a few minutes, Bundle of Holding is going to release an Old School Bundle. Their previous bundles have been quite interesting -- this one is actually right on target.
The way these things work is bizarre, but it apparently works. I think that people "pay what they want" at the beginning, but as the average price moves up, that averaged price becomes the minimum. I think that's how it works, anyway. There will no doubt be instructions.
It is an inexpensive way to pick up pdfs, and I'm the author of a couple of them.
HERE IS THE LINK, which will hopefully work after the preview page is done and the bundle actually starts