Why is there a Burning Rubber Smell Under my Hood After Driving?

If that’s the problem it should be fixed w/due speed, otherwise the engine compartment gets gunked up making future repair and service more time consuming, and it could cause the engine oil level to go below the “low” mark on the dipstick between changes.

Re the cost, depends on the engine configuration. There’s a another thread here about Honda Accord valve cover gaskets.