CBS, home to “60 Minutes,” the “CSI” franchise, “Two and a Half Men” and the new hit crime drama “The Mentalist,” is having a better year in prime time than any other network.

And yet, as at the other networks, profits have declined sharply at CBS.

For decades, the big three, now big four, networks all had the same game plan: spend many millions to develop and produce scripted shows aimed at a mass audience and national advertisers, with a shelf life of years or decades as reruns in syndication.

But that model, based on attracting enough ad dollars to cover the costs of shows like “Lost” and “ER,” no longer appears viable. Network dramas now cost about $3 million an hour.

The future for the networks, it seems, is more low-cost reality shows, more news and talk, and a greater effort to find new revenue streams, whether they be from receiving subscriber fees as cable channels do, or becoming cable networks themselves, an idea that has gained currency.