Mega Project Rankings (USD Inflation Adjusted)
The New Deal: $1T,
Interstate Highway System: $618B,
OpenAI Stargate: $500B,
The Apollo Project: $278B,
International Space Station: $180B,
South-North Water Transfer: $106B,
The Channel Tunnel: $31B,
Manhattan Project: $30B
Insane Stuff.
It doesn't look great so far :)
However: 1. That has no bearing on how much they actually spend, which is what was being discussed and 2. Neom is much more than just The Line. As you can see from the YouTube link I posted, Sindalah seems to be on track to open this year, which is part of Neom.
So while Neom overall might be behind schedule (and The Line or other components may never open), it is clearly not an "imaginary" project given that parts of it will open soon.
If that were the case then Stargate is already a thing because OpenAI must have a data center somewhere already.
And yes, the plan was for it to be 170km, since it was announced.