I won't offer much more than an acknowledgement on this topic tonight for lack of time. The main point to be made is that these costs are a very strong function of our regulations, and our regulations are both incredibly strict and inconsistent.
Opponents of nuclear power often attempt to confuse the issue, acting as if nuclear waste does not already exist. They'll complain that Yucca Mountain is insufficiently analyized or otherwise inadequate without ever acknowledging that it's the best we have. It certainly is easier to secure waste at one site than the dozens and dozens we have now, yet instead of seeking the incremental improvements they would have us remain in a state that is worse. Incidentally, have you read this?
As for decommissioning plants themselves, how clean is clean? That decision alone would raise or lower the costs by entire orders of magnitude. Opponents of nuclear power want the area restored as if no one had ever set foot there, but there simply isn't any logical reason for that. If it was a good site for a nuclear power plant, it's probably a good site for another one - rip out the parts that are past their useful lives and start over. The cooling is there, the power lines are there, the staff is there, the seismic analysis is there, the emergency plan is there - why throw this all away?