It's been a minute since I was researching this, but from what I remember, Reolink showed up the most for me.
If you can get your hands on older Ubiquiti camera's, G1 and G2 I believe, you can install their NVR software on any server.
Or you could always go the route of using a Raspberry Pi and basically making it from scratch, I know pishop has several camera modules and cases with different features, and if you were fine using WiFi, a Pi Zero would be enough to make it work.