What is the approximate cost to replace a head gasket on my 2012 Volvo S60?

What is your question?

On my 2012 Volvo S60, there is an oil leak; what is the time and costs to replace a leaking head gasket which the mechanic says is needed?

What makes this problem better or worse?

There is an ongoing oil leak on the floor of my garage

How long has your 2012 Volvo S60 had this problem?

Since I bought the car a year ago I have been adding a quart of oil roughly every 1000 miles