For Japanese people, since ancient times the number eight has been sacred. They believed that the number had special powers. Even in modern times people considers the number 8 as lucky number because the shape of the kanji “八” for it looks like spreading wide toward the future, which is believed as a symbol of prosperity.
When you read the Kojiki and Nihon Shoki, “Oyashima” (the Eight Great Islands which is a reference to the shape of the Japanese archipelago, the “Yata-no-Kagami” (a sacred mirror which is one of the three sacred treasures), and “Yasakani-no-Magatama” (another one of the three sacred treasures) all reference the number eight. Furthermore, “Yamata-no-Orochi”, “Yakumo”, “Yaoyorozu no Kami” also use the number eight in their names.
Eight is even used to represent the idea that “there are many numbers” or “a number that cannot be counted.”
Also, when western version of number 8 is turned on it’s side the number takes on the meaning of infinity or multitude.
The sentiment of “may happiness visit everyone” is present in the blessed rice, and since the number eight is connected to good luck it shall be sold at 8 dollars.