By far the cheapest source of supplemental magnesium I have found is epsom salt. Any pharmacy sells it by the pound for just a few dollars. Epsom is magnesium

By far the cheapest source of supplemental magnesium I have found is epsom salt. Any pharmacy sells it by the pound for just a few dollars. Epsom is magnesium sulphate heptahydrate (MgSO4·7H2O). The molar mass ratio of epsom to Mg is about 10. Thus, in order to get 350 mg of elemental magnesium, you would take about 3.5 g of epsom salt, which is a little less than a teaspoon. The taste of epsom is completely hidden by almost anything you put it in. I mix it into tea or juice.