These are two rather difficult questions for this forum. First, no one here would be able to put a $ figure on the value of your rifle case ( though it would be interesting to see a photo, if you posted one). For that you need a dealer. Though, you might find a completed auction on GunBroker or Ebay of something like it, that might give you an idea of the value.

Second, the genealogy of your family always starts with you : from there you work backwards. It's a very common mistake to assume that two people who share the same name will likely be related. They often are not, and the only way to avoid that is to go backwards, step by step. There are genealogy sites that can assist you greatly in a search. You might also try the Union Co NJ Historical Society to see if there are more records of the Ogdens and Caldwells, especially if they were substantial property owners. If your search is within the 19th c., it's possible there are good surviving records.