Here are some deals, FWIW.
Frog God probably has the biggest sale ATM. Some titles - both 5e and OSR - are 60% off. Not sure what to pick, since I'm not into megadungeons and detailed settings. Maybe Monstrosities and Tehuatl.
Some of my own books are included in the sale (I don't know how they chose it).
Old School Feats and Alternate Magic are compatible with B/X and OSE, BFRPG, etc. They add lots of options to your games without getting to AD&D/RC levels of complexity, and you can check the free previews in the site to read almost half the books.
I also have a couple of "get everything" bundle for 50% off, but these are not Black Friday deals:
And here are some deals I've recommended in the past and are currently on sale:
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