Feline Fanatic is right, you'll need a certified appraisal. Even then, the shipping company will balk at paying out on any insurance claim. Many quilters who ship their quilts have a fine arts rider added to their homeowners insurance, and don't get additional insurance through the shipper. Not sure how it would work for an item for sale, though.
The appraisals on my quilts have cost around $50.
Janet