I think you're assuming too much. Yes, it's a safe assumption that under a la carte, everyone would pay for fewer channels. HOWEVER, I think you're making a huge jump in saying the total cost would be less. It might for some folks, but I'm guessing as a general rule, most people will pay about the same as they're paying now.
It would be a huge "jump" if I were just guessing as you seem to be. But we don't have to guess. We have the facts of the channel providers' behavior to tell us which is true. (See my argument above.) They really really believe that they are getting the most out of their properties by bundling lots of nearly worthless channels; that's why they do it; that's why we don't have a la carte already.