Replacing coil and spark plugs?

Hello,

Typically when the valve cover gasket or the spark plug tube seals goes bad you will have oil on the plugs. Which will require replacing the gasket as well as the plugs. I have attached a picture of the valve cover gasket for your reference.
The coils might need replacement depending on condition.

Here is a helpful guide on valve cover gasket replacement:

https://www.2carpros.com/articles/replace-valve-cover-gasket

As for the cost it will depend on the parts they will use and the labor hour rate.
Did they give you a break down of the costs?
Replacement of the valve cover is about 1 hour labor.

Let me know of any questions.
Thank you.