As of 2015, the average cost to replace spark plugs ranges from $129 to $166, most of which consists of labor costs. The price of the spark plugs themselves typically ranges from $9 to $14.
One of the first signs that spark plugs may need replacement is the appearance of the check engine light. Spark plugs that are failing may cause the engine to misfire, which may make this light come on. If this is the issue and a person continues to drive, it may damage the catalytic converter. Catalytic converter replacement is much more expensive, ranging from $539 to $872. The parts for this repair range from around $340 to $620.