There was a similar thread last year.

I pay full fare quite often. Mostly try for something cheaper but often you get a week's notice to fly transatlantic and all the nice fares are gone. Last month, I had to change a ticket to fly back from SEA instead of JFK just days before the flight and the cost of the change was madness because only full fare business was available. I opted for the semi-flexible F on the return leg instead which was much cheaper