The rent really depends on areas and apartments' establishments.
For example, the average rent of typical 1room+kitchen apartment in Chiyoda-ku is 122,000 yen/month. Chiyoda-ku is where Imperial Palace Gardens, Tokyo Station, Akihabara, etc., is located. On the other hand, the same establishment would cost 62,000 yen/month in Edogawa-Ku. Edogawa-Ku is the easternmost ward of Tokyo. Further cities such as Hachiouji-City, which is on the west side of Tokyo, approximately an hour train ride from Shinjuku, the average rent is around 50,000 yen.
More info on this website: https://www.homes.co.jp/chintai/tokyo/city/price/
You can find cheaper apartments if you don't care oldness of building or facilities inside the apartment; such as no kitchen or shared bathroom/toilet.
Also, shared residences are quite popular in Tokyo which is cheaper compared to regular apartments.
For 1 person in the center is about 80,000¥~12,0000¥. In Tokyo but not at the center will take at least 50,000¥.
Or you can find apartments around Chiba or Saitama, it’s not only close to Tokyo but also from 50,000¥ you could find a better room than in Tokyo.