By default, every Synology NAS device you purchase allows you to link up two different cameras to the device for free. For a small home setup, that might be ok, but if you need to add more cameras to the system, you need to purchase licenses and they run roughly $50 per extra camera.
I have three cameras and so had to purchase an additional license. But it was just one-time, fairly painless.
Here too, very solid and reliable. I believe this info is still accurate:
I have three cameras and so had to purchase an additional license. But it was just one-time, fairly painless.