Fusing together a gram of a 50/50 mix of tritium and deuterium produces as much energy as 10.000 liters of gasoline. Priced at $1 a liter it costs $10.000 while half a gram of tritium costs $15.000. This on top of the insane capital costs of a fusion reactor, which will likely be 10 times higher than a fission reactor of the same power, while using a fuel more expensive than gasoline per energy content.