How much does magnesium cost per gram?

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, (as 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)