For comparison, the federal government is dead bent on building additional 4.1km of highway through Berlin that is estimated to cost over 500 million. And the critics say it will balloon to billions since the estimate is 10 years old anyway.
So basically millions of people will ride the train for three months for almost free, and the cost will be in the same ball park as 4km of one highway.
Also it is really ridiculous because it goes straight through a rather central part of the city, removing old construction and very close to where a lot of people live in an attractive part of the city.
Instead they could build it a couple kilometers further out to still connect the ring, the distance in drive time would probably be less than 5 minutes.
But they stick to stupid plans they made 10 years ago like they always do in this city.
The city doesn't want it, the federal government is pushing for it. Probably because the person in charge is a free market theologist from FDP so he wants to spend as much tax money as possible to have as little impact as possible. Wait, that doesn't make a lot of sense, but it's what's happening.
So basically millions of people will ride the train for three months for almost free, and the cost will be in the same ball park as 4km of one highway.