Cheap surge strips have components that degrade with each surge. They degrade to the point of no longer offering protection and give no indication of their state. I prefer a good ups, but higher priced surge protectors have a different kind of circuitry in them that does not really degrade. IMHO, spending $40 or $50 for a good one that will last for years is far better than replacing a $12 one every year or worse yet, not replacing it and having no protection at all.
A ups can handle sags as well as surges (low voltage can be harmful too). Some models have very good line conditioning for clean power. All but the cheapest can also shut down your rig if power fails, assuring the proper shut down of the os without corrupting files.