Never eaten the buffet breakfast at the Sofitel... I guess that it would be pretty exepnsive - about £15 a person... in general, hotel breakfasts in hotels in this country are not worth that much (unless you manage to get a "breakfast inclusive" rate.
When we have stayed at the Sofitel (well, Le Meridien as it was then), husband has normally popped across the connecting airbridge, to the terminal, and picked up a couple of MacDonald's breakfasts. I am not a big MacDonald's fan, but their breakfasts are ok and the cost is good.
Boo