The real question is how cheap are the machines to run?
Say Kodak decides tomorrow to stop making all film. They just stop. SOMEONE will buy up their plant or at least the machinery in it and take up production. They will be able to get the used equipment cheap. The real cost will be running the factory to make the film. If you can do it cheaply, you are set.
Now, the actual cost of a box of film is probably more related to what people will pay than to how much it costs to make. There is no reason 10x16 should be more expensive than 12x20. Rather the opposite. But if the market will bear a high price for the "rare" 10x16 then they will sell it at the high price.
I am pretty sure that sheet film is cut down from one large roll. It just seems odd not to do that when you can get a whole lot of different formats from one roll. With 35mm and 120/220, I think they each come off special machines. 35mm seems to have a thicker base to me (very unscientific statement here by the way) and all 3 formats have different numbers and codes on the base. So it would seem that they are coming from different sources.