But where did you take those grid cost numbers from? Iter costs are <100bn AFAIC; and Germany alone (!!) projects more than that (top end) for grid expansion/operation within 2040 (mainly north/south and offshore connectivity).
For the material cost, just applied maths. By sheer coincidence, 1Ω of aluminium around the world is very close to 1m^2 cross section: https://www.wolframalpha.com/input?i=40000km+*+resistance+al...
This is almost exactly 1e8 (100 million) tons: https://www.wolframalpha.com/input?i=40000km+*+1m%5E2+*+dens...
This is $223bn at current prices: https://www.wolframalpha.com/input?i=40000km+*+1m%5E2+*+dens...
For scale, this is about what China makes in 2 years; if this is rolled out over 30, which would be optimistic but plausible, it's within the realm of just how much China increased production between 2023 and 2025, being spent every year.
To get to 10x ITER's own estimate for ITER, the wikipedia page says the organisation estimates the reactor will cost about €18-22bn: https://en.wikipedia.org/wiki/ITER
There are a lot of reasons not to do this as a single big 1m^2 "wire", amongst them being that the surface magnetic field is strong enough to be dangerous to approach with ferrous materials.
But because Nimbys have no appreciation for beautiful pylons, projects in that direction are doomed for now anyway and everything needs to be buried underground at extra cost :(
Pylons… eh. Doing this realistically rather than my napkin-maths, it would be a mix of many different solutions in different parts of the world, from competing environmental issues. Some would be pylons, some underground cables. Is the Sahara dry enough to run it on the ground, or in a concrete trench? I have no idea.
As a side note, every so often I keep being surprised on here by Americans who can't rely on the grid in winter because snow disables it, and some Californian forest fires are attributed to unmaintained pylons failing, dropping live wires onto the forest where they spark and light up the dry wood. These could both be resolved by burying more cables. Likewise within urban areas: here in Europe it's rather rare to see overhead lines in urban or suburban areas, unless they're over a tram/railway line.
IMO the real killer of any project like this, is geopolitics, not local politics. EU doesn't trust China, the US, or Russia; the current US administration doesn't trust or doesn't like basically everyone; Russia kinda gets along with China but few else; China would like to sell stuff to everyone but also have border disputes and other friction with many of their neighbours.
