A lot of the costs is politics, and second-order effects from lack of production lines making everything a one-off.
Which "funnily" enough makes it so that the more dangerous reactors remain in use for longer, as the new designs aren't built, despite huge safety improvements (even if you go just for late 1970's self-sealing molten lead/bismuth reactors).
Overcapacity is a problem, especially for low-enriched reactors, but that's why it shouldn't be the only answer.
Which "funnily" enough makes it so that the more dangerous reactors remain in use for longer, as the new designs aren't built, despite huge safety improvements (even if you go just for late 1970's self-sealing molten lead/bismuth reactors).
Overcapacity is a problem, especially for low-enriched reactors, but that's why it shouldn't be the only answer.