Wouldn't the first country achieve this be in huge / leap forward advantage? Especially for a country like China with lots of Production and Exports.
There will also be staffing costs, fuel costs (small, but still — deuterium and tritium aren’t free), and even costs associated with obtaining cooling water.
The big benefits of fusion over fission, as I see it, are that the fuels are safe and plentiful, the byproducts are harmless (if neutron activation is well managed), and the reactor itself isn’t full of extremely dangerous materials. If you turn a fusion reactor off, it’s off, and there’s no risk that it accidentally keeps reacting.
However, maybe a fusion reactor may be used for fission bomb research, but I'm not sure how.
No doubt some time in the first few years there will be some unforseen new kinds of maintenance requirements and failure modes to discover.
Given complexity and high material stresses, fusion reactors will also likely have very high operating costs. DT reactors, in particular, will require replacement of major structural elements every few years due to neutron damage.
In contrast, the cost of installed utility scale PV is around $1/W.