[Tade0]

A kilometre of a 1GW HVDC ground line costs $0.7-1mln. Double or triple that for sea lines[0].

China has had 2000km+ lines online for years now, so there's precedent. Not for solar specifically, but plainly to connect distant grids.

We have huge fiber optic connectors wrapping the planet, so there's precedent here as well.

Overall a global solar grid is technically feasible and actually not terribly expensive, but we need to solve the political issues preventing it first.

EDIT [0] for comparison highways cost $4mln per kilometre in the US and double to triple that in the EU.