Cost estimates are just that - estimates.

I've only just become aware of the Sphere in Las Vegas, a 20,000 seat performance space. What interests me is that it was proposed as a $1.3 billion project that ultimately came in at around our over $2 billion.

Yes, megaproject cost overruns occur in the private sector, too. It's not just a government problem, although the problem may be exacerbated by the lack of need to turn a profit in the private sector and the ability to keep on tapping the public for more funds.

The causes of the Sphere's cost overrun are normal. A long developing process is at risk of unexpected shit happening during that long period of development - in this case the pandemic and subsequent supply chain problems and inflation.

But even more, the uniqueness of the project - bespoke projects almost always cost considerably more than expected. For any large innovate project, just assume at least double the cost - you're likely to look like a prophet.