What is the cost of magnesium in pounds? The cost of Magnesium per pound is $2.45 per pound. The price will vary depending upon the purity and the form of the magnesium required, and the quantity being purchased, (a…s buying in bulk tends to result in a lower price for a given mass of product). The chemical supplier Sigma Aldrich will give prices for various forms of magnesium and in various quantities. As an example: 500g of granular, reagent grade, 98% pure magnesium would cost £43 (GBP) 2kg of granular, reagent grade, 98% pure magnesium would cost £144.10 (GBP) 5 people found this useful.