I don't struggle and feel lucky about that, but don't have lots of money.
But the pads can only bought by the axle set. So why not replace them all? It can't be a money issue because you can't buy just one side at a time.
I replaced the pads on my new-to-me truck this past fall. Every year or so, I like to get in and clean up and lube the slide pins and the brackets as rust usually seizes either the pads or the caliper from moving properly. I bought pads, they were the wrong ones, but the ones on the truck were in great shape with enough meat on each that they looked brand new. Rotors looked brand new as well. But the brackets and slide pins still needed to be cleaned and lubed.
Such is life in the rust belt.
As far as doing one side only, that would be for an emergency repair only. IE you're on the side of the road and need get home or a repair shop.