I was told by folks on this forum to get a refurb Dell Optiplex from the dell us outlet store. They come with 3 years onsite warranty. I just bought an optiplex 7040 with i7-6700, 16gb ddr4, 250gb ssd nvme for $670. Look up the configuration you want and call a rep. More discounts. paid $55 for 1TB purple HDD and thats where I hope to save the recorded data.
Edit: No graphics card. I was told it's unnecessary and consumes more power. This is an optiflex small form factor.
Costco has deals on the XPS 8900 and I think they add a year on the warranty. I was going to get one until someone reminded me that an NVR PC needn't be large and expensive