Renting/buying broadcast space on digital platforms

I understand this might not be a professional approach towards it, but I'm wondering the methods of how television companies gain broadcasting space on Sky Digital/Freeview/Cable providers; as in, average rent costs, maintenance costs, methods of contact, methods of acheiving the space.

This is relative to a dream I had last night about it, possibly after seeing blank spots on Freeview. No idea why I had this dream, but it would be nice to know how it's possible, if anyone has any idea of the basic methods.