Thanks, SHJ. It hadn't occurred to me that there was such a thing as a computer breakers' yard. I've found a couple of websites based on your suggestion. I think this is going to be a much cheaper way to do it. I'll still have it replaced by a technician, but sourcing the parts either in the US or UK, or even buying used rather than new, might save me a bundle.
Two questions if anyone can answer them for me, please:
I have a 2006 MAcbook white. Will ALL Macbook logicboards fit and work in it?
Is there any real risk in installing a second-hand one from a reputable source?
Many thanks,
Shawn