Since you consistently wrote about a "ship chronometer", I assume it is something like this:
and not this?
Generally, it is impossible to give an authoritative indication of an old timepiece's value: Too much depends on the age, the movement's condition (while a slightly damaged box normally only barely compromises the value), and also the presence of the paperwork. If the chronometer had been issued to the naval forces of a nation, then there were many documents that confirmed it being handed over, the various service dates (marine chronometers were very frequently serviced, at least every two to three years), the ships it was issued to, and so on. If this paperwork is complete, the chance of the chronometer being sold at a higher price is larger.
Those chronometers are normally not sold at Ebay and similar auction sites, but more often at auctions by dedicated auction houses, such as Antiquorum and Sotheby's. I would suggest to either let their staff estimate your timepiece, or to follow some auctions, to get a feeling for the prices paid. Unfortunately, Antiquorum has discontinued its former user-friendly practice to offer a searchable database that permits access to all past auctions at once, together with the auction results.
Regards,
Marcus