'Poltergeist' Clown Heading to Zak Bagans' Bedroom, Haunted Museum

Holly Madison is gonna loooove this ... her BF, Zak Bagans, just dropped a fat stack on the famous clown from "Poltergeist," and wants to keep it in his bedroom!!! The "Ghost Adventures" star tells TMZ ... he threw down a cool $80,000 at an…