1. if the price of salt … (to go) up 10% you … (to pay) extra amount rather than … (to go) without salt.

1. If the price of salt … (goes) up 10% you … (will pay) extra amount rather than … (go) without salt.
1. If the price of salt … (goes) up 10% you … ( pay) extra amount rather than … ( go) without salt.
1. If the price of salt … (went) up 10% you … (would pay) extra amount rather than … (go) without salt.
1. If the price of salt … (had gone) up 10% you … (would have paid) extra amount rather than … (gone) without salt.