To be as honest as possible with you, it is the same answer as "how long is a piece of string". To knock out a rear wall, correctly support it, add basic patio doors and make good I would say £2.5-£3k. Bi fold doors alone can cost £2k+
As for the kitchen this is complete guess work. £5k -£50k.
Virtually impossible to answer with any accuracy I'm afraid. Just make sure company knows what they are doing with the wall removal.