I think it boils down to two factors:
1. Take as much as you can get. Why would the contractors do the job for 2 billion when you can get 5-6 billion?
2. If the team(s) owner(s) want this to happen, it becomes very easy for the person/people running the project to say we can make your dream come true for 2 billion...then reality strikes..and you're 2 billion into this project, your team needs a place to play, the whole thing is a national punchline..so you just shovel money at it
I'm sure whatever happens, even if the taxpayers didn't agree to fund any of this, they're going to get a big bill for this project.