That's an uncommon chambering for the New Service. I think the gun is refinished, which would bring its value down. An original .44 Russian New Service was offered for sale on an Internet site at about $1800 not too long ago, but I don't know if it sold. I would think this one might be fairly priced at about half that, but I'm not an expert. The fact that it has adjustable sights is a big plus and may boost its value.
You might post on the Colt forum if you haven't already. There are some very knowledgeable guys over there.