InArt charges about a $100 premium for rooted versus sculpted so that seems to be market rate. The ArtToys Edward Scissorhands rooted is about $150 more than sculpted.
Like you mentioned, I don’t know the true value or expenses involved.
I sent my Sansa Stark (GOT) head sculpt to an artist to get rooted a few years ago - IIRC, that was at least couple hundred (if not more).
but that Sansa root job was a custom one-off to my specifications (not assembly line like Hot Toys) and you’re paying the artist for the labor, time, materials, etc. And Sansa has some semi-complicated braids to replicate.