The "Ghost Adventures" star tells TMZ ... he dropped a whopping $50k after a crime collectibles site put the bifocals up for sale. The glasses are also believed to have been worn by Bundy when he abducted 12-year-old Kimberly Leach in Lake City, FL, back in 1978.

Along with the glasses, Bagans got the original brown evidence bag complete with the exhibit tag ... and a crime scene photo showing the glasses inside the Volkswagen Beetle Bundy stole before he was pulled over, and finally arrested for his heinous crimes.

You can now guess where all these items are headed -- Zak's Haunted Museum in Vegas.

As you know ... Bagans has tons of creepy stuff, including this, this, this, this and, oddly enough, this. And, just like all those freakish items ... the glasses will have their own, specially designated area.

Bagans tells us the glasses will be behind a jail exhibit, made out of real jail bars. He says, "It's incredible to know that the eyes of pure evil looked out of these glasses at his victims and the pure hell of what these glasses saw."

He adds, "I shall forever keep them locked up inside my Haunted Museum's real jail exhibit where they belong!"