If the City didn't need to borrow money for the project -- i.e. if revenues kept up with costs all the way through -- there would only be construction costs and no financing costs.  In that case the project cost would be about $8.2 billion. The City has cited this figure pretty consistently during the session.

However there ARE financing costs, which VARY depending on the revenue source. The excise tax surcharge produces steady, slow-growing revenue that falls short of construction costs during much of the construction period, but continues on after construction ends. So paying for rail with the excise tax surcharge requires lots of short-term borrowing, which adds interest expense, which bumps up the total project cost to around $10 billion. A hotel room tax increase could generate more revenue faster, decreasing borrowing and lowering interest expense.

The legislature's indecision on a revenue source is what's moving the numbers around, yet Saiki blames the City.  Ah, politics.