Mmm... "thousands" eh? That's a lot.
I once got quotes from plumbers to move a toilet from a different room into a bathroom and install a new basin. Thousands. Then I pulled of a couple of sheets of plaster off the wall and got a quote from another plumber to put a pipe from here to here and join it in here. Hundreds.
There are companies that could hard chrome the crank pins and re-grind them oversize - certainly the parallel ends (with the pins) need doing, not clear about the tapers on the outer ends (if there are tapers). This is their bread and butter and wouldn't be too expensive. I'd guess 100-200 pounds, but maybe more these days. There are also toolmakers who could open the holes in the crank with appropriate accuracy, again 100-200 pounds? (just guessing). Maybe they could make new pins for less than the cost of hard chrome + regrind. Then sort out big end bearings, with an inner pressed onto the crank pin and an outer pressed into the rod - another couple of hundred pounds.
So it could be done, and "you" could do it by taking the various jobs to the people who perform the individual tasks. But to be on top of the over-all job, you need to be the expert measuring and specifying exactly what you want so the job will work overall. It's hard.
This is why your man says "thousands" to do the job. Is Alpha Bearings still doing jobs like this? Worth asking. Converting currencies (I'm in Australia) I'd be very happy is someone quoted me 1000 pounds, and wouldn't be surprised by 1500. As a non-expert machinist, but a pretty good measurer and specifier, I reckon I could do it (for myself) for half that, using expert services to do the actual jobs. Of course there are restorers who are also expert machinists as well as expert measurers and specifiers, and they would do the job (for themselves) for a lower cost again. But what value their expertise, machinery, and time? We're back to "thousands"!
Leon