Do you still own a Synology?
Pretty sure you get one Camera registration free.
Pretty shitty that you have to pay to register cameras on your own server.
(I really like Synology, but this is one thing that I don’t like about it)
This would give you a self hosted, internet connected, app accessed option and you can choose your own cameras.
Details
Purchase link (4 Camera)
https://www.amazon.com/Synology-Camera-License-Pack-CLP4/dp/B001JD8J8W
I haven’t tried or tested it myself, so I can’t give a personal reccomendation