SH wrote:
You mention you had just a valuation? I'd be thinking about having the
full survey done.

I'd have thought the surveyor would be able to provide a ballpark price for
underpinning, given the situation they find. That would likely be more
accurate than any random number we might generate.

If there's anything dubious about the structure then a proper survey would
be worth its weight in gold, I'd have thought.

FYI, for what little they're worth:
https://job-prices.co.uk/underpinning-house/
https://www.myjobquote.co.uk/costs/underpinning-a-house

Theo