It is impossible to purchase a single aluminum atom. Even if it were possible, the cost would be so small as to be negligible. Aluminum is a very common metal, and the price of aluminum is based on the cost of mining and refining the ore, not on the number of atoms in the metal. As of January 2023, the price of aluminum was around $2,500 per metric ton. This means that a single aluminum atom would cost less than a billionth of a penny.