Green Energy

DEMO is not a singular reactor, but rather a class of reactors that are expected to be built using the technologies and lessons learned from ITER. So basically ITER's main goal is to be a massive international R&D project to pave the the way for individual countries to be able to build their own DEMO plants afterwards. Pathfinding manufacturing technologies for this unique of a system is a big part of why ITER is so expensive. Replicating an ITER like machine should be considerably cheaper.

Although I personally wouldn't be suprised if commwealth fusion systems SPARC/ARC leapfrogs ITER/DEMO. Unlike a lot of fusion startups, their approach isn't particularly novel, which means there shouldn't be major physics surprises. The higher field intensity afforded by REBCO should mean much smaller and cheaper machines.