When I said I'd prefer no WiFi, I meant I don't want it to be connected to the internet, I don't need to upload video, nor do I need or want to record and store data in the cloud. I do like the idea of wireless cameras for the flexibility of location selections, but it's not essential. My existing system's monitor plugs into the wall and the cameras have wired connections to it and that's ok.
About my comment re: Wi-Fi use: I'd rather not use my home cable-connected Wi-Fi for this; we seem to have enough trouble keeping our TV's, PC, laptop and iPads all in synch and working properly. If I were to acquire another Wi-Fi router just for this I'd need to connect to the same cable network, right? Sorry for the dumb question, just confirming my assumptions.
Yes, basically you could just buy a router to be standalone, and if you wanted it to be connected to your network you could do it via Ethernet or a wifi bridge. Given that you seem to be having instabilities with your other devices, I might just upgrade to a slightly higher end router that may improve your performance/stability issues, and lets you securely manage everything from one spot. Likely improves your security posture a lot, and simplifies things. I think at that point, you could probably have a little less heartburn over having the cameras on your network.
But that's getting a little beyond the scope of this topic though...I would still probably just do something like Pete's eBay link.