An important question, but one that cannot be answered. It just can't. Fine china is different than precious metals, diamonds or other commodities. These have set prices per ounce or karat which are set by certain market forces. China on the other hand has no intrinsic, raw material value. It's value is strictly based on it's popularity and the demand for it at any given time. Therefore there is no set value for china pieces, even for dealers. A dealer who has 24 place settings of Bing and Grondahl Seagull will pay a fraction of what the dealer who has two place settings will. On the other hand Wedgwood Kutani Crane is so sought after that it will always command a good price.
There is no set price for china pieces or sets. The only way to get a ballpark figure as to how much you will get for it is by pricing it out. Contact dealers, check out Ebay to get an idea. Then decide based on price and other factors such as shipping and reliability as to whom you would like to sell you china to.