[jasonbvr]

The name of the onsen near Nikko I forget, but if you take the bus up to Kegon Falls that is where the onsen is. Prices, I don't know off the top of my head, but I do recommend Nikko Park Lodge. Run by a Buddhist monk, he offers a full vegetarian dinner at night and morning meditation session.

Ballpark estimate, you could do both for around 50k yen. Transit, not shinkansen, 20k. Four nights stay, 20k. Food, 10k. I am totally guessing too. Any tourist office is going to have pamphlets for Nikko in English. There is one in the base of the Tokyo Metropolitan Offices (Tou-cho in Japanese). Transportation may actually be less if you go round trip by overnight bus. You can get an overnight bus to just about anywhere popular from Shinjuku station.

My recommendation for travel info is japan-guide.com