When sourcing magnesium bars, the price is primarily driven by purity levels, typically ranging from 99.9% to 99.99%. Higher purity commands a premium due to the intensive refining process. Additionally, consider the physical dimensions and weight (e.g., 100g, 500g, or 7.5kg ingots), as smaller, precision-cut bars involve higher labor costs. Ensure the supplier provides a Material Safety Data Sheet (MSDS) and a Certificate of Analysis (COA) to verify chemical composition, specifically limiting impurities like Iron (Fe), Copper (Cu), and Nickel (Ni) which affect corrosion resistance.