The cost of fixing a misfiring engine can vary depending on the cause of the issue and the extent of the damage. In some cases, a misfire can be fixed by replacing a single component such as a spark plug, which may cost around $100. However, if the misfire has caused significant damage to your engine, repairs can cost upwards of $1, 000 or more. It is best to have your car inspected by a professional mechanic to determine the cost of repairs.