Gazle, I just checked Nikko Tourist association's website - they list the fare for a hired taxi to drive visitors for 5 hours to visit: Toshogu, Rinnoji temple, Futarayama shrine, and Chuzenji hot spring. The quote was 26,500 yen for a regular sedan taxi.
They say they have "saloon bus" (I assume a minibus) or "jumbo taxis" (I assumee a van) as well, but those would cost more.
(Website in Japanese)
http://www.nikko-jp.org/access/taxi.html