Exchange rate in this post: 11 USD = 1,000 yen. : Breakfast + lunch: $20
... sounds to me a bit too low.
It depends on persons and on where you have a meal / buy your food, but I think it's not always possible for me to get a well-balanced breakfast / lunch for 1,000 yen (about 11 USD) in Tokyo.
20 USD per day may be enough if you take a fast food shop breakfast and a convenience store box lunch every day, but may be not enough if you have every meal in a restaurant on a department store's upper floor.
: Train fare: $10
: $50 per person for the trip should cover both admissions and a possible Sumida River boat tour.
10 USD per day sounds enough for fares of JR, Tokyo Metro subway and Toei subway.
Fares in taking Yurikamome Line and/or Rinkai Line (both running via Odaiba) are relatively high.
A charge for Sumida River cruise widely varies depending on courses. If you have a chance to see a special exhibition in a museum or so, its fee can easily surpass 10 USD. I think it's better to count these cost separately.
: the JR line that runs from Shinjuku to Tokyo Station
Yes, that's Chuo Line. (Pronounced like "chew-oh line.")
Local trains in principle do not run via Tokyo, while no rapid trains run through both Chuo and Sobu Lines.
- Shinjuku --{Chuo Line}-- Ochanomizu --{Chuo Line Rapid}-- Tokyo: 2F. Tokyo: B5F --{Sobu Line Rapid}-- Kinshicho --{Sobu Line}-- Chiba.
- Shinjuku --{Chuo Line}-- Ochanomizu --{Sobu Line Local}-- Akihabara --{Sobu Line Local}-- Kinshicho --{Sobu Line}-- Chiba.
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