The cheapest aluminum alloys are typically those with lower purity and less desirable properties compared to higher-grade aluminum. Among the commonly available aluminum alloys, 1000 series alloys, such as 1100 and 1050, are often considered the least expensive. These alloys have relatively low strength and are primarily used in applications where corrosion resistance and formability are more critical than mechanical properties. However, the cost of aluminum can vary depending on factors such as market demand, production processes, and alloy composition. It’s essential to consider the specific requirements of your application when selecting the appropriate aluminum alloy to ensure it meets your performance and budgetary needs.