If you can not afford to spend handsomely on your spark plug purchase but still want to get the good ones, you can always go for the ones with copper construction. Copper is the least expensive spark plug building material. The products with copper construction have a tip made of copper, which is highly conductive and offers a vital spark for ignition. However, when it comes to endurance, copper is a soft metal. It erodes away quickly due to all the heat & pressure applied to it. You can quickly expect a copper plug to last around 20,000 to 30,000 miles.