I'm a huge fan of Frog God Games' Swords & Wizardry releases. The current Swords & Wizardry RPG Mega Bundle at Humble Bundle has some really nice picks, even at the $1 Bundle level.
At the $1 Bundle level, the titles that stick out to me are 1975 (Bill Webb), Against Tsathogga (Skeeter Green), and The Riot Act (James Spahn), among other titles.
The other sweet spot is the $18 Bundle level, which adds in City of Brass, Grimmsgate, Hall of Bones, all seven entries in the Hexcrawl Chronicles, and How Orcus Stole Christmas, among a total of 62 titles.
The level to avoid is the $38 bundle. You don't need a physical book that was a secondary part of a Kickstarter over a decade ago.
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