From here, a model by Nefashu, http://www.planetminecraft.com/project/minecraft-world-in-a-bowl/, at a safe (but expensive) 2 mm/block. Note that the inside's hollow, both to make it cheaper and to make it cooler (you can peek inside the hole). I've added no markup in cost to the model (no money for me), this was just a cool model and I thought I'd give it a try. Anyone can download the model and put it up at their own store (hint, hint, Nefashu).