While I don't think they will jump from $5 to $50, I don't think ala carte cable would save much money. The movie channels are ala carte and range from $7/mo to probably around $20. But that is usually a package of movie channels. You don't get one HBO, you get four or five.
Unbundled channels means fewer subscribers for most channels. Using Nielson numbers, it looks like about 103 million of 114 million households have cable/satellite. Would unbundled cable bring in additional subscribers? Possibly. But many more would opt out of channels too. If ESPN has 100 million homes at $5/mo, how many will they lose if unbundled? Surely there are hippies out there who could care less for the Yankee-Red Sox-Tebow channel. So if they lose 10% of households, they would have to raise fees by approximately 10% to maintain revenue. Not a huge jump. But what if they lose more than that?
And, unable to compete, many channels would fold. Fewer channels means less programming. Every so often, I enjoy watching a show on the Science channel or Animal Planet. But would those channels exist with fewer subscribers? There probably wouldn't be AMC to air Mad Men. Would it air on another channel? Yes. But, if no major channels picked it up originally, one would think it may not have been developed in the first place.
Finally, bundling also adds costs to the cable companies. Maybe most of it can be done online but there will be more customer service techs needed. Which are costs passed down to consumers.