I'd have to say it depends on the cartridge. If it is available at a good price, and easy to get, than reloading may not pay off. If the round is not popular or common, then reloading may be the only way you can get ammo. I've just gathered all the components and dies for reloading my .56-50 Spencer carbine. I understand there is loaded ammo available but the price is high.
More commonly I reload for my .375 Winchester and a .41 magnum, neither of which are cheap if you rely on factory ammo. If I were shooting a 5.56 I would probably be happy shooting a lot of the commercial ammo out there.