I've been meaning to give this a try.

https://github.com/gtxaspec/wz_mini_hacks

So far as I'm aware with that software "installed" on the camera (which can be removed simply by removing the SD card) you should be able to set up the camera's with standard local access and block them from the internet entirely.

Its a thing I plan on trying out in the near future, but it works like it should then its like a $45 (CAD) wireless(ish) security camera. Which isn't bad.