The CBO looks SSBN(X), the successor to the Trident boats, and estimates that the cost will increase from $7.2 billion to $8.2 each:

The Congressional Budget Office is out with a new estimate of the Navy’s latest 30-year shipbuilding plan, issued in February. While that new plan reduces the total number of ships purchased between 2011 and 2040, and thus shipbuilding costs, CBO says the annual price tag is still much higher than the total shipbuilding funds the Navy has received in recent years.

The Navy’s new plan calls for buying 276 ships between now and 2040; the previous 30 year plan called for 296 new ships. Still, with the annual shipbuilding budget at around $15 billion (the average for the past three decades), the Navy can’t afford to buy all of those ships, CBO said.

We need to start with cost targets as the most important driving requirement for defense procurement programs, followed by schedule, and any other issues must be secondary, or this sort of cost creep will continue ad infinitum.