Agreed regarding the cost. Mineral supplements are grossly overpriced. Essentially any mineral supplement can be found in bulk (pounds to kilos for $10-$30) and at a purity equivalent to food grade even if it is not marked as such. Some can be found at the grocery store and the rest at Amazon.
Borax, the sodium salt of boric acid is more soluble and safer than the boric acid found in capsules, the latter being sold to kill insects. A $3.00 box of laundry borax used to boost detergent for clothes or dish washing is pure enough and will last a lifetime.
The same is true for my $8 one-ounce jar of iodine crystals. It was sold at the feed store so that one could make one's own antiseptic solution for horses. My horses never needed it and as a supplement the jar of iodine crystals will outlive me. I recollect that smaller quantities may be found at REI to purify water when hiking. One must grind a tiny mass of iodine crystals into a rather large amount of salt to dilute it but a batch of powder serves me for 1-2 years.
Amazon has food grade sodium or potassium nitrate sold to cure meat which is a fine NO supplement. One can also order potassium bicarbonate (mix with sodium bicarbonate) to correct blood/urine PH. The same goes for Magnesium citrate, a much better supplement than magnesium sulfate (epsom salts).
The big gun for a potassium supplement can also be found in the grocery store. Morton packages 20 pound bags of potassium chloride chunks for use in water softeners for about $12. A decent spice grinder turns the chunks into powder.
Right now, I am experimenting with lithium and strontium salts.