APC makes good UPS's..what you want is line filtering, and a battery backup. Got one at Wally World for about $100..they're pretty good at what they do (have one on this computer)..small world, I used to do computer support for FPL (back when it was CP&L), fixed their servers, and they used APC's..in 7 years, 1 died, out of hundreds..so go for it.
Computers do have some filtering circuitry, but it's mainly converting the external AC to internal DC (what the motherboard runs on). Thing about large spikes, is that they degrade the protection circuitry over time. The 'power protection'ones that look like power strips work ok..but only for small work (actually, mine looks like a power strip, only it's about 3 times that size.;).
The important thing the battery gets you is a few minutes to save your work and turn off the PC.
After all the hurricanes you've had, the problem sounds like it might be on the outside of the house..power companies 'play' with the voltage all the time..sometimes they 'brown out' industrial areas, like on the weekend, particularly if demand is high..residential sections are supposed to get first priority. Good luck, hope the voltage settles down down there soon..

I wish I'd said that.. The Staircase Wit

anahl nathrak uth vas betude doth yel dyenvey..;)