The offer is tiered with the lowest tier starting at $1 and containing the Pathfinder Beginner Box, the core rules, several sourcebooks and trial access to Pathfinder Online. The next tier starts at $8 and contains additional material like the Advanced Player’s Guide and the Villain Codex. The third tier starts at $15 and contains books like the Ultimate series of sourcebooks, Bestiary 2 and 3. Last but not least the highest tier starts at $18 and contains more material for Pathfinder, and also the core rules for Starfinder, Paizo’s new Science-Fantasy RPG.
Of course you can always decide to pay more. Each Humble Bundle sold supports charity. You can either choose the one featured by Humble Bundle this month, or choose your own.