Condition, maker, age, decorative value, rarity, and your location, all go into the pricing of an antique clock.
I think for appraisal in your area you should find someone who deals in and repairs antique clocks in your area.
You can try a site like this one to see if it can help you determine value
http://www.antiqueclockspriceguide.com/
but it may be more cost effective to buy one of the many books out there or peruse your local bookstore or library for volumes on the topic.
You may find this general site on the topic useful too
http://www.e-grandfatherclocks.com/
My husband works with antique clocks doing case repair pretty frequently for a dealer who specializes in them and from what I've seen over the years you need an in person exam by an expert who knows the local markets to figure out actual value.
Hope this helps you!
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