Replacement cost of 100+ year old pearl necklace

My home was hit by a tornado and I am trying to get a replacement cost on a pearl necklace that I inheirited from my great grandmother. The pearls were 7.5 in size, the necklace length was 18" and there was a silver clasp with a small pearl mounted on top. I would appreciate any estimates. Pease e-mail me at rosellabeckmannATgmailDOTcom