Martha Berry founded Berry College in Rome, Georgia. It began as a boys industrial school in 1902. A girls school was added in 1909. It became a college in the 1920s and was granted full accreditation in the 1950s.
Please do not store your old letters in the attic or basement but in a closet in the living section of your home. Place each letter in an acid free paper or plastic envelope, acid free file folder, or archival acid free document box.
While I can not tell you the exact value of your letters, you could find some information, or consider donating the letters to the Martha Berry Digital Collection. You can find them online.
If you want to have them appraised, locate a local professional through the American Society of Appraisers. Expect to pay $50.00 - $60.00 for the service.