C&H rifles and shotguns over the years have gotten a very bad rap. In all honesty they kind of deserved it. If you look at the bulk of English gunmakers today the locks are very similar in many ways. They copied each other and some added the best features of several different types of locks. Not Cogswell! They wanted to be different and they are! Their locks seemed to be completely different from all other makers and that is OK if they are fairly reliable. When a problem arises in a C&H gun it is usually a real pain to repair. Due to this fact, they are more expensive to fix than the other makers rifles. They do have problems that will surface and you have to be willing to pay the price to have them repaired.
This said, I would estimate that your rifle would have a value in the range of 6800.00 to 7500.00. Finding a buyer may be a little more difficult than normal but I am sure that there is buyer out there somewhere.