How handy with tech are you?
I have a setup using Raspberry Pi’s and the camera modules.
I think it cost me about £40 for each of the pi setups (it was a few years ago) and I then installed MotionEye for free, which can send alerts, cycle data, store on remote storage, only record on activities etc, and also only record when motion is detected. If you feel like it, you can also use that facility to hook into the GPIO outs on the PI to trigger external responses, i.e. lights, alarms, opening a lion cage etc.
Records to a an external hard drive attached to the router, and due to the nature of a Pi, you can either use ethernet, or you can buy a cheap WiFi USB adapter.
It was actually very easy to setup, as long as you can work out how to write an image to a Pi, as there are load of pre built images out there. Can also be set up to use a normal IP camera as another source, and has a reasonable web interface.