This headline is a bit odd and doesn't represent the original title nor article content. What does "within budget" mean here? That it costed what the original budget set out to cost? Couldn't find anything related to the budget within the article.
It was indeed built within 27 years:
https://infrastruktur.oebb.at/en/projects-for-austria/railwa...
It is mostly within budget, estimated in 2005 were 5.5 billion €, total cost as of today are 5.9 billion €, the difference being largely attributed to the pandemic and later addition of sections.