I'd add that that, for this calculus to work out in a straightforward way, a competitive market is necessary but not sufficient. You also need other factors that help drive economies of scale, such as the thing in question being a manufactured good that can be sold to many people, or the production requiring expensive and specialized equipment that can be used for more than just that one thing.

I'm no expert, but I'd guess that these factors are more likely to line up in manufacturing and construction, or even R&D, than they are for things like maintenance of specialized IT systems or administration of services.