UPS aren't really cheaper.

Sure, up front you're paying very little for that box that can run your PC for an hour.

But over 2-4 years you'll have to replace that UPS after it fails catastrophically in really dumb ways, and that's if you're lucky and it doesn't also burn your house down, whereas a proper storage system will last for a long, long time with more capability.

In my business I've never had a deskside UPS live longer than that.

And yes, we don't buy the ultra expensive ones. That's true.