I believe it might be reasonable to calculate the cost of production as follows:Assuming that we had the engineering drawings, equipment, and trained artisans in place, then it might be fair to compare our "new" Elcee to one of the new Ruger doubles.
Granted, we're comparing a true sidelock to a boxlock, so we'll add a bit of leeway for the increased cost of such. We'll also add a bit for the level of fit and finish we might expect from our "new" Elcee.
I notice that you specified "by hand". The Elcee, though a production gun, really was a hand-made product. Very few parts will interchange without hand fitting. I'll assume this new product to be "hand fitted" instead of a scratch-built as the cost of such would be astronomical.
Hand fitted, but made in a production facility with the intent of equaling a 1913 "00" in numbers that would justify somewhat economical manufacture ? Probably in the $3000+ range to a consumer at minimum. So much depends on the hidden factors. Liability, setups, materials, and engineering to modern standards, taxes, etc.
Consider that the "00" was somewhere in the neighborhood of $40.00 in 1913. A working man with a reasonably good job would see a wage of $400.00 per year. Double that for a really good job.
Compare this to a $30k wage today, or a $80k wage for some of the better-paid jobs out there. What you'll see is an increase by a factor of about 10x. This takes me very close to the numbers quoted.
As I stated above, the real secret lies in numbers. Past a certain point our new Elcee would become cheaper to manufacture. Before that point the cost would escalate as numbers became fewer.
A very interesting question. I'll be interested to see what others will say.