The most economical backup is a $20 penn plax air pump that comes on when power fails. It uses two AA BATTERIES and will last several days running.
I use a 75A power converter used in rv’s and charge 12vdc batteries. Because I have extended systems, I run continuous 12VDC air pumps with no switching device. For systems with sumps, I use an inverter to run AC PUMPS, again no switching devices. All diy.
Know this about Uninterrupted Power Supplies, I use them for life support systems only. If you want to operate everything, then get a whole house generator.
I have an anker solix battery backup. It has little wheels, so I roll it over when the power goes out and it can run the main return pump for like 30 hours or so. The ideal option is a natural gas generator, quote was 13k for an install though.
Battery backup air pumps that come on automatically on power loss, UPS for flow pumps, generator for longer outages (half of the house with heat plus fish room).
Ecoflow river 3. Less then $200. Built in UPS if the power goes out. If you have bigger demand, just size up. Ensure you pick one that has UPS feature. For longer outages the generator just kicks on.