Seems like I read somewhere that Marcel Thys of Belgium was / maybe still is, building doubles for G&H.
If that is so, I would guess prices begin at least around 30 thousand US dollars for a rather plain one but, the Marcel Thys double rifle I examined (Best Grade .470 with ejectors, and spare .375 H&H ejector barrels) appeared to almost rival my favorite maker's best grade doubles (Westley Richards) in fit and finish - ALMOST.
I cannot recall what the owner wanted to sell that very special two barrel set rifle for but, I think it was 40 something thousand dollars and that was about 12 years ago, of course it was not new at that stage either.
He had hunted in Tanzania with it but had then decided he wanted to sell it afterward.