All of that requires a lot of capital, but what makes it expensive is the neutron flux ruining it in just ~5 years.

Yes, the steel required to withstand the force of the magnets, and to be dense enough to prevent hydrogen from leaking, magnets powerful enough to contain thebl fusion reaction, cooling systems to keep the superconducting magnets in close proximity to the neutron rain at extreme low temperatures.

These are all the parts we know about. Then, there are all the systems that no one has attempted yet that you will need to actually extract some energy from the whole thing, and to inject fuel into the running reactor, and to recycle tritium.

Overall the reactor vessel has to be built similarly to a high-pressure submarine, but it needs to withstand even higher forces. Not exactly something that can be done cheaply, even though we have been building submarines for a good 50 years.