Look at the new stretch of Shinkansen from Aomori to Hakodate.  All isolated tracks running in culverts, elevated guideways, etc, and lots of tunnels, capable of supporting trains running at 160 mph, and maybe faster in the future.  The Japanese managed to do that 93 mile stretch for $4.7 billion, which is about $50 million/mile, or about 10% of what the Honolulu rail is going to cost, IF it manages to come in at $10 billion.