In fact $13 billion is a rock bottom estimate of total costs from project inception in 2006 to project completion and full commissioning into revenue service in 2026 (or later.)
If HART rail were to start operations today, it would get about 20% of the expected opening day forecast ridership.
Unlike a large metropolis with huge demand for commuting trips (where rail makes sense), HART rail will be a costly and environmental disaster for decades.
The only "solution" is to cut it short. Complete 16 miles to the Middle Street intermodal center and stop the bleeding there.
Many thanks to Dr. Keli'i Akina and the Grassroot Institute of Hawaii for the ThinkTech interview.