Well, Brookline today is $3.20 a mile whereas my yardstick Washington Flyer (to from IAD) was still $2 a mile this summer. Other Boston suburbs probably similar to Brookline; your numbers suggest ~$3 plus toll. The suburban taxi will also charge you the ~$5 toll for his return since he cannot pick up at Logan.

NYC is $2.50 so Boston area is quite expensive like most things in Mass. DC used to be $1.50 until 2012. My guess is that $2 is still average for the US.

The Tokyo fare is about $5 per mile.

So the fare from Narita to Shibuya-/Minato-ku is probably more than 25,000 yen on the meter but I think they always discount 10% on long trips. But then there are also tolls of ~2,500 yen to Shibuya. MK Taxi charges 17k yen flat fare plus tolls and parking, claiming it is 40% off the meter rate. Tokyo Airporter is 20k all inclusive, which is the best deal.