As with pretty much ...

As with pretty much everything, "costs" and "efficiency" really depends on what you want to obtain in the end.  What is the acceptable final water quality is the FIRST question.  Then you can look at the relative costs of different systems.  If a "high end" system is required to obtain a particular quality, then you can really compare that cost to a very simple particulate filter system.  Simpler/fewer filtration result requirements will be less costly than the more exacting methods.  "Efficiency" can really only be compared between systems with similar outputs.  Select a standard unit of comparison - Volume per time per purity - and then you can compare system costs by normalizing that value to different systems with similar quality output specifications.

I have not seen "side-by-side" comparisons anywhere, as most comparisons focus on the differences in delivered quality or similar unit comparisons.  Only the user can decide which quality parameters are essential to see how different system "efficiencies" might be compared.