The concept of being able to watch what I want, when I want (which to me is the inevitable future of television) is hugely valuable
EDIT/addendum:
Wow... honestly I would pay out the nose for the convenience of being able to watch what I want when I want in a format that I'm already accustomed to (couch+TV). Hell, not only would I pay for a subscription but I'd also be willing to pay for incidental usages much like renting a movie without having to go out and find it.
If you include live local news and other local and live shows (so that it TOTALLY replaces all other forms of television), maybe up to $100/mo. I'd rather be able to tune it fully ala carte however, so that I don't pay for anyone's sports or other crap I don't use/watch, and then get it for something closer to $20-50/mo.