Allan Sutton, a friend here in Denver, is reputed to be one of three "authorities" on all things related to early recordning technology (of which 78s and cylinders are included). He has a Web site with links that can probably tell you the value of what you have. He has books and complete discographies of some labels, which can help determine age, value, etc. Some discs, (of course the really rare ones), can be worth quite a bit of cash, well into the tens-of-thousands. Typically, anything recorded acoustically will be worth more (before 1928 or so). I don't know how much classical was recorded acoustically, the few classical records I have were done electrically. There is a huge difference, technically and sonically, and special care should be paid to playback of each type of disc (stylus size, weight, etc).
Good luck!
M
Mainspring Press