What if the construction cost of the fusion plant is so high that the electricity price is not competitive? That's already a concern with recent fission reactor projects, where the investors demand price guarantees from the public.
That is a valid concern, if perhaps a fusion plant requires the outside be coated in platinum or something. It would have to be both expensive and difficult to manufacture/obtain. It is essentially where we are today with ITER, which is to say if ITER generated net power it would still be a hard pill to swallow if it costs $100B per power plant.
Fortunately, many of the significant costs the plague fission plants (like the legal expense of dealing with all the lawsuits, the cost of unlimited insurance, Etc.) would likely not apply to fusion plants.
Fusion reactors will be both much larger than and much more complex than fission reactors. They will necessarily be more expensive, even if they aren't made of resublimated unobtainium.
The size difference follows from limits on heat transfer through the first wall, and has been known for 35 or more years.
