Basic/Cheap Camera System - Setup Help Requested

Hello everyone! I am hoping some of the resident experts here can give me some guidance on getting a camera system setup.

Recently, I got suckered into taking over a position for our HOA (Someone quit and a friend on the board was in a bind). We have a camera system at the pool, that apparently hasn't worked for almost 3 years. They asked the company that installed it to "fix it"; the company bought a brand new NVR (Without asking), then 4 months later sent a $1,000 bill. With my new found power, one of my first acts was to sent the NVR, and the bill, back to them.

There are 4 IP cameras with the wires pulled back to a central closet. I am thinking I can setup a server with an old computer I have laying around, install some free monitoring software, use a small switch for the cameras, and that will be that. I am looking to do this cheaply, and most importantly, with as little work from myself as required.

I couldn't get the model camera, but the NVR is NVR716NS-P. I am thinking I can use the onvif or one of those open video outputs to setup the server?

Anyone got a good guide or place to start? If not, I will probably just buy 4 Wyze cameras and stick them out there.