You might opt for a business hotel near Tokyo station. If you're comfortable with a tiny, no-frills room, you can find a cheap business hotel for about 10,000 yen around Nihonbashi - within walking distance of Tokyo station. If you go up to 20,000 yen, you can be in a livelier area -- Hibiya (REMM, or the Dai-ichi Hotel Annex) or Ginza (Mitsui Garden Hotel). You might also want to look at the Hotel Metropolitan Marunouchi, which is right on top of Tokyo station. (The buildings around Marunouchi aren't so Japanese in ambience - but you can go to Nihonbashi for some old-style izakayas, and the Shin Marunouchi building has some more modern bars and restaurants that stay open very, very late).

Other areas that you could consider:

- Nippori Station is easy to reach (by Keisei Skyliner) and puts you in reach of the "old Tokyo" working class neighbourhoods. Hotel Lungwood sounds awful, but looks OK. (Remember also that the Keisei Skyliner is cheaper than the N'EX).

- Shinjuku Station is somewhat less accessible than Nippori and Tokyo, but it's as lively as Tokyo gets. (N'EX runs less frequently to Shinjuku and takes 90 minutes - compared with 60 minutes to Tokyo station).