It's a large chimney and repointing is a tedious, labor intensive process, so the quoted price does not seem unreasonable. It may be worth getting some additional estimates but remember that a good repointing job requires carefully chipping away the old deteriorating mortar - this process is much more time consuming and difficult with stone than with brick - before new mortar is placed in the joints.

New mortar will be a lighter, unweathered color, but there are mortar colorants that should make the difference less obtrusive.

Thanks for replying :)
Yes, they told me they could add color to the cement.
There are few chimney companies in my area which I would trust, this one is someone I've worked with before and was very happy with but I surely will call in at least 2 more just for comparison's sake.

One of my contractors has a mason that did work for me already (rebuilding front walkway brick steps), he was quite easy to work with. I suspect, however, he'll be more money as his quote for repairing my chimney box was more, but perhaps not.

I'd like to get it done within the coming year. I took a good look at it a couple of weeks ago, and while there is nothing falling off, nothing crumbly, etc. I don't like all the fine lines I see and better safe than sorry.

Oop meant *firebox :)

I am curious who you are using. I got quoted $3k to repoint a chimney that is only exposed above the roof line, about one quarter of the area yours is. I am also in Northern NJ.

I never went ahead with the work! Every quote was SO far out of affordability. Luckily the chimney has been holding up. It hasn't gotten worse, nothing is crumbling off. I think the highest quote was like $9K, lowest around $6K.