Prices are set in advance by contract between the co-op members and the producers, and they don't change no matter how good or how bad the harvest is. This protects both the consumers and the producers, because the former promise to buy a fixed quantity, and the latter guarantee to sell at a fixed price.
而購物金額早在訂會員與生產者契約時就已決定，不論收成好壞都是一樣價格，這樣可同時保護消費者和生產者，即「全量購物和費用保證」。