'Star Wars' & 'Harry Potter' Gear Going Up For Auction

Fantasy and sci-fi movie geeks are about blow serious wads of cash on memorabilia ... including Harry Potter's actual Hogwarts acceptance letter and an X-Wing (miniature) model used to shoot 'Empire Strikes Back.'

TMZ has learned that London's Prop Store is putting original props and costumes from iconic film franchises up for bidding next month. The 'Star Wars' and 'Potter' pieces are expected to fetch top dollar -- $80k to $105k for the X-wing model .. and $4,000 to $6,500 for the Hogwarts letter.

But there's a ton of other movie stuff available too:
- Scar Predator costume from "AVP: Alien vs. Predator"
- Mel Gibson's "Braveheart" sword
- Sloth's mask from "The Goonies"