Phantasmagoria: A Puzzle of Flesh. This sequel to Roberta Williams' adventure-thriller (which is also available on GOG) will only cost you $5.99. And for just six bucks, you'll be getting a whole bunch of crazy.
The game follows the exploits of pharmaceutical engineer Curtis Craig, a former psychopath who begins to suffer vivid hallucinations while seemingly being framed for murder. During these hardships, Craig also begins to explore his own sexual preferences, leading to a multitude of on-screen sadomasochistic encounters. Also, zombies.