Octomom -- I'm Buying a DUNGEON with Masturbation Money

Octomom has deep, dark plans for the money she's earning with her new solo masturbation video -- telling TMZ, she wants to buy a "dungeon" with the cash ... to keep her and her 14 kids safe from the prying eyes of the public.

Of course, "dungeon" is a metaphor -- what Nadya Suleman means is she wants to buy a house that's far away from everything ... preferably in a low-key gated community ... where she can "hide."

Octo was on her way into Makeup Mandy in West Hollywood this week -- to get a spray tan for her big shoot -- and she told us, "The only dream I have is to buy a safe home for my family."