Lol @ £1k.
I'm going to say you'll see quotes around £4-5k, depending on materials.
Supply the materials yourself, surely. That's what I did. He doesn't have to get a local (ie: central London prices) builder in.... sometimes it pays to get someone in from outside the area.
1K probably isn't doable, but depending on scope of works, he quite possibly could get it done under 2.
You can make it as expensive as you like by going for expensive materials but if you're happy with something that does the job and looks OK then you'll save £££s....