you could use PoE cameras with PoE switch which used APC's UPS to protect the power. I'd also recommend having your NVR backup to the cloud. In the case of Ring devices, it's part of the subscription.
Buying new UPS sometimes is unnecessary, I bought mid-tier SMB ups from APC on eBay for a song
APC SUA750 Smart-UPS 750 Battery Backup System for $50 shipped. Buying used ups pretty much guaranteed that the batteries won't last long, BUT buying decent aftermarket batteries on amazon is possible.
Other than APC I'd also suggest TrippLite as I generally have good experience with their products.
Besides UPS capacity (and fancy features which you'd never need) where is one which could be important protecting computer equipment and it's Pure Sine Wave.
A decent explanation is here:
Shopping for a UPS? Two types exist—and their respective output waveforms do have an effect on the equipment they're backing up.
blog.tripplite.com