NodeBB is open source software. It is free for anyone to download and install on their own server under the terms of the GNU General Public Licence (GPLv3).
If you are looking for a service to host your NodeBB forum, we recommend DigitalOcean. They charge based on your usage, but you can get a month of free hosting from them by following this link.
Self-hosted NodeBB users are not eligible for our support services. If you have questions, please feel free to visit our community forum. We have a very active community of users and developers who may be able to help you out.
NodeBB also offers commercial server licences, hosting and enterprise customization plans. Please see our pricing page for more details.