For up to 80 percent off.
The entire "Doorways" franchise is currently on sale on Steam until December 21, 2015 as the "Week Long Deal:"
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Doorways: Chapters 1 to 3 Collection - $4.79 (70 percent off).
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Doorways: Prelude - $1.99 (80 percent off).
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Doorways: The Underworld - $3.49 (65 percent off).
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Doorways: Holy Mountains of Flesh - $4.99 (50 percent off).
The Doorways: Chapters 1 to 3 Collection includes Doorways: Prelude (a.k.a. Chapters 1 to 2) and Doorways: The Underworld (a.k.a. Chapter 3).
Also, please note that Doorways: Holy Mountains of Flesh is currently an Early Access Game.