Home security camera systems can be expensive. But where there is a Raspberry Pi, there is a way. All you need is a Raspberry Pi Zero W, a Raspberry Pi camera module, some free software and an enclosure that you can buy for as little as €5 (~US$5.57).
https://www.notebookcheck.net/HKCam-A-Raspberry-Pi-powered-and-open-source-HomeKit-security-camera-that-costs-under-US-20.422731.0.html