If shouldered by the individual, an extra $1k over a few months, plus however much it costs to keep re-testing, and the cost of supplements or better food to correct the deficiency, is a staggeringly insurmountable cost for the people who need it most—the poor.

As you say, this directly impacts day-to-day wellbeing. It's exactly the kind of thing that should, if it's even moderately effective, be provided free of charge for every human being.