I would imagine the expense is difficult to determine and quite controversial. Especially when you consider the costs of the effects to the ocean/environment and whatnot that aren't being borne by the japanese people.
Any nuclear accident is unacceptable, but what do you think the rate of crashes were in the first 1000 Airplanes?
When we don't build nuclear, we don't really get better at nuclear. If the U.S. decided to build 50 Nuclear reactors in relatively remote parts of Nevada to power California. Even if we had another accident, by the time we had finished that project our safety standards would be in a very different place.