Were actually thinking of doing something similar at the minute, Its a timber frame and drywalled wall so not load bearing, I also need a rad moved.
Were just looking to make the acrhway in the partition wall so not the whole wall but wouldnt imagine the price would be much different.

I have a builder getting me a quote so should hopefully know this week, Ill let you know.

I would have no issue making the doorway myself but the radiator being relocated may involve floors needing to be dug up so thats not something I am interested in tackling myself.