Replacing a head gasket can be expensive for a few reasons. A blown head gasket can often damage other engine parts, like the water pump, which may also need replacing. The job is fairly labour-intensive, requiring technicians to strip off most components around the engine. The head gasket can warp under the heat of a failure, so once removed, the technician may send it for skimming, which is when a small amount of material is removed to make it smooth and flat again. Not skimming the gasket could result in another failure.
Matt Wrankmore
Head of FixMyCar's Garage Network