Mastodon is used by me alone and costs ¥1590/month.
Misskey is free with OCI for less than 5 people.
PieFed is ¥491/month.
Lemmy is the biggest server in Japan, but I host it at home because it has about 5 MAUs.
(Unfortunately, it is not popular in Japan.)
Media is R2, but it is still within the limits of no billing.
I probably post frequently.
File servers and multiple BOTs are also running.
It may be a little expensive, but it is a typical amount of money for a VPS that runs Mastodon somewhat comfortably in Japan.
SAKURA internet VPS
※Sorry, I'm using machine translation.