I remember that thread too and the poster worked in some capacity for an AD if I recall. If my memory serves, he mentioned the cost of the parts- sans donor movement and cost of service/assembly was in the range of $1.6k (not sure if there was a dealer accommodation discount applied to that total). That would indeed be a little cheaper than buying a second hand Watchco provided the donor movement and cost of service/assembly was less than about $1k.
“Watchco” has become the generic name for any build like this- and there is no provenance or branding associated with the builds that came from the company Watchco except for the early ones which are rumored to have been SM300 born movements that can be proven with an extract...key word is rumored.
Paying a premium for a watch that was built by Watchco is simply a misunderstanding of what those watches were- they were all “franken” watches if by Franken it’s implied that the movement didn’t come with that case/dial/hands. But all parts are from Omega, so other than it not coming directly from Omega as that exact build, they are all the same- be them from Watchco or an independent with a SG account.
One of our resident Omega cert watchmakers made the point in that thread that it doesn’t go against any Omega policy and that an independent Omega watchmaker with a Swatchgroup parts account could in theory do this if a donor was provided- but questionable if Omega themselves would do this at a customer’s request.