I am in a place where electricity is not ideal (old house, no ground), sometimes it occasionally shuts down and supposedly there are some spikes.

I consider using UPS with the goal to increase safety of my personal data. My first priority is the health of my internal and external USB hard drives which can be damaged due to possible power instability. I do not care that much about possible losses of not-saved work, instead I just want to let my system have a minimum time to turn off without any risk of physical damaging my hard drives.

Would a cheap offline UPS suit my neads? Or do i need a better one with automatic voltage regulator (AVR)? How critical is AVR for the hard drives? The external ones require their own power supplies and will be plugged directly into UPS.