When are you going? Because times are also different during holidays, make sure you check your time in google maps and the tobu website
Google maps:
https://www.google.co.jp/maps/dir/Asakusa+Sta.,+1+Chome+Asakusa,+Tait%C5%8D,+Tokyo/Nikko+Station,+4+Aioich%C5%8D,+Nikk%C5%8D-shi,+Tochigi-ken+321-1413/@36.2283978,139.1971188,9z/data=!4m14!4m13!1m5!1m1!1s0x60188ec690127e2f:0xf41f021a3a02cff0!2m2!1d139.797676!2d35.7107111!1m5!1m1!1s0x601fa0c50058feb7:0xaa70a4403876bb73!2m2!1d139.62204!2d36.747448!3e3?hl=en
Tobu webpage train timetable:
http://www.tobu.co.jp/foreign/en/access/nikko_kinugawa.html
Info about the trains: http://www.tobu.co.jp/foreign/en/news/20170418.html
This is the new Tobu express train launched in April 2017. If you use this train, you can leave from Asakusa
Revaty Kegon・Revaty Ryomo
I am not sure of the cost, but I would save around 3000 yen for the trip just in case.