How much would a three or two week trip to Japan cost?

I was interested in spending about 3 weeks in Japan. Either Spring 2025 or Autumn 2025.

Ideally I wanted to stay for 23 days. 1 day there, 3 weeks staying, 1 day travelling back. I might also consider changing it to 2 weeks(plus 1 day there and 1 day back, 16 days total) instead of three if that's simpler and a lot cheaper.

I am mainly going as I like anime, enjoy the pop culture and like the cultural aesthetic. I also have a couple friends I am going to see. Anime, games, temples, cafes, restaurants, izakayas etc.

I would be flying economy of course. And I wouldn't book a super expensive hotel or accommodation but I would try to find a decently clean comfy room with a shower(think about Premier Inn level of quality) would be my preference. And of course spending money while there for food, fun and souvenirs.

At most I could spend £4000 in total. Ideally I'd want to spent less than that. Would this be enough for a 3 or 2 week stay in Japan? Or how much is realistic.