The best source for a good appraisal is Bernard Levine. He's an expert with several books published (the best known one is The Guide to Knives and their Values, 4th Edition). He's very professional and well respected, so if you're interested in insuring or selling your knives his appraisal services will be well worth the money (his rates are sensible).
Here's his contact info:
PO Box 2404
Eugene Oregon 97402 USA
Gerbers from the '80s are quite desirable, especially if you've got the boxes and paperwork.