YOU SAID:

it costs nothing to be kind

INTO JAPANESE

親切にすることは何の費用もかかりません

BACK INTO ENGLISH

It doesn't cost anything to be kind.

INTO JAPANESE

親切にしても何も費用はかからない。

BACK INTO ENGLISH

Kindness doesn't cost anything.

INTO JAPANESE

親切には何の費用もかからない。

BACK INTO ENGLISH

Kindness doesn't cost anything.