I compared costs of various drops and things to change water to alkaline (not comprehensive but compared the simplers methods and products). Found that WaterOz brand alkalizing drops are the same strength per dose as the "big brand" that is highly promoted on the Web, and much, much less expensive per dose. It is stronger than that other brand, so need fewer drops. My two dropper bottles of WaterOz brand have lasted me nearly a year! I don't always take the same number of doses per day, so can't do the math there, but if you do a search on the WaterOz, some of the sites selling it state the dosage and you can calculate from there.
I think I got mine from herbalremedies.com, but there are a few other places for it. Hopefully other brands will come along to add to these two, because how much technology could this really take to make water alkaline? Note that this brand is not a mineral supplement, that would be an entirely different topic.