Determining the value of 78rpm records can be difficult. The UCSB library cannot provide appraisals or advice on the value of your records. But short of hiring an appriaser, there are several resources available that can help you determine the value of your 78s and cylinders.
A good introduction is "The Value of Old 78s—With Comments on 78 RPM Price Guides" by Tim Gracyk.
Les Docks’s book "American premium record guide, 1900-1965" is available in many libraries and bookstores and provides guidance on record values, but is limited primarily to jazz, blues, and hillbilly 78s. Classical and popular 78s are not covered at all.
Some auction companies publish "prices realized" lists. Nauck’s Vintage Records is one such company.
Finally, you may not find the exact titles you have in your collection, but browsing eBay (especially completed auctions) by label or artist can give you a sense of what similar items are selling for and is a fairly reliable guide to the current market for 78s and cylinders.