I think Matt from MiniWarGaming mentioned in one of his videos that they paid 2500 dollars per master miniature when they were making the Dark Potential game.
I presume that must include full commercial reproduction rights and their line is fairly unique, i.e. not easily convertible from something else.
Michael Perry can whip out a Napoleonic grenadier in no time flat, partly because he's done tons of them and partly because he has things like suitable dollies, equipment masters etc. ready. Sculpting something totally new from scratch based on a verbal description or concept sketches is much harder.
If you just need a single, there's no sense on making molds. Just pay to have it converted or even sculpted from scratch and paint the original.