Now of course that's a research reactor full of experiments and instrumentation that wouldn't be part of a normal power plant, but given current experience that I think we can expect we won't suddenly knock down the cost to $100M. It's going to be somewhere in the billions. And we have expectations of that DEMO is going to make 750MWe.
We can then plug those estimates into the calculator and basically figure out how cheap and how powerful a fusion reactor has to be for it to make economical sense.
The size and also the complicated governance have made ITER very slow to build, which also increases expense. The JET tokamak is about the size of the reactor CFS is building, and JET was built in a year for the reactor itself, plus three years before that for the building they put it in.
It took us a lot of time to standardize computers. We made lots of weird architectures before things settled down.