Nobody has a clue, because we haven't figured out how to build a reactor that generates net positive power at all yet. The cost of the fuel is trivial, but ther

Nobody has a clue, because we haven't figured out how to build a reactor that generates net positive power at all yet. The cost of the fuel is trivial, but there's no telling how much it will cost to mass-produce and maintain stuff like superconducting magnets, high-grade vacuum systems, whatever we end up using to contain the massive neutron flux, etc.