What cheap camera doesn't require a phone app and serves RTSP out of the box?

Note that I didn't say "cheap". If price difference comes from manufacturer's hope of selling its cloud service, then the time and effort required to set it up is not worth the money.

If I were to solve one-time task of keeping an eye on someone indoors I would go with USB camera (if lighting conditions allows even the laptop's build in), which is going to be cheaper than ones with IP and WiFi support.