The ninth chapter of mishnayos Bava M'tzia had numerous cases in which someone is working someone else's field, whether as part of a sharecropping agreement or under lease. Most of them do not indicate the price. Some do so so as to indicate that the agreement was for a fixed price rather than a percentage. And then there's mishna 10, which lists a price for no apparent reason:
הַמְקַבֵּל שָׂדֶה מֵחֲבֵרוֹ לְשָׁבוּעַ אֶחָד בִּשְׁבַע מֵאוֹת זוּז הַשְּׁבִיעִית מִן הַמִּנְיָן. קִבְּלָהּ הֵימֶנּוּ שֶׁבַע שָׁנִים בִּשְׁבַע מֵאוֹת זוּז אֵין הַשְּׁבִיעִית מִן הַמִּנְיָן.
Someone who [rents] a field from his fellow for a septennial (one shmitah cycle) for seven hundred zuz, the sh'mita year is included in the count. If he got it from him for seven years for seven hundred zuz, the sh'mita year is excluded from the count.
Why does it mention the price?