NYC is actually the textbook example of most expensive places to run new fiber, due to needs for nearly 100% underground, and extensive pre existing utilities. I'm going to guess you've never been involved with an outside plant fiber project.
Do they need to run their own fiber - is there a way they could rent fiber space from an existing line? At least for a little while?
Don't be worried that a new player has entered the space; be worried that the existing ones haven't improved the space. The total market space can be increased by creating new connections, and someone has to do it.
Get large enough, and you can start carrying other traffic too, and eventually start buying/laying fiber. But you know this, it's probably part of your business plan.