Is changing the price of a computer device based on different installment periods (6 months: $900, 12 months: $1000, 18 months: $1100) considered unlawful, or is each of these options considered a separate contract?

If there are multiple options for selling a computer device based on its various capabilities, the interested buyer must choose one of them, and it is not permissible to conclude a sales contract while hesitating in the choice. It is permissible to increase the deferred price beyond the cash price, and it is permissible to state the cash price of the sold item and its price in installments for known periods. The sale is not valid unless the contracting parties firmly decide on either cash or deferment. If the sale occurs with hesitation between cash and deferment, it is not legally permissible.