What will it cost to fix an intake gasket link on a 2001 expedition with 173,000

What is your question?

A small amount of steam was coming from under the hood of my truck. I had my brother-in-law look at the problem and he said that I had a intake valve gasket link. He showed me where the coolant fluids were linking down in the valley pan underneath the motor. This problem just started yesterday and I haven't driven the truck since. Is this a major problem and I hard is it to fix. Should I go to a shop or let a backyard mechanic mix it?