What would be the cheapest way to sleep in Tokyo without having to travel far away from the city center? Some basic comfort level is expected so sleeping in a back alley is excluded.

By "city center", I mean the big connected areas like Tokyo Station, Shinjuku, etc.

I have a decent enough understanding of japanese to conduct basic conversation and orient myself around.

My guesses are either couch surfing or sleeping in 24h manga cafes, but I would like to know if there are other options.