Having never owned an AIP or even seen one in person, I can't say this with authority, but I suspect that this is not a genuine Grant AIP, or at least not one made for D&D and sold as a limited edition. If I'm not mistaken, on his official limited-edition AIP bottles made for card companies, Grant uses lamination to seal the "card tag" in hard plastic and prevent it from getting damaged over time. This "AIP" has the card inside a cheap film-like plastic sleeve, like the type used to protect inexpensive gaming or sports cards - the sleeve is completely open at the top.
Grant did say that he does commission work - you send him a deck, he'll AIP it for you. But there are restrictions on this. It's not beyond the pale that this might be a genuine Grant, but it's being passed off to look like some sort of official limited-edition D&D release. If I remember, he charges around $100 for the commissioned work, which would be a good reason why this seller is asking so much for this one. He might have a genuine commissioned bottle, but a bogus hang-tag to make it look like a legit ltd. ed.