If it has been stored well it should be an exceptional older Champagne. Won’t be too bubbly and will have some mushroom and possibly slight Sherry characteristics. But really a great great wine for aged Champagne lovers. If you have some way of supporting a claim that it has been stored properly it is also worth over a thousand dollars retail. (Probably around $1000 private sale.) Without some proof of storage conditions, though, it probably wouldn’t sell for even a couple hundred.