While purchasing and setting up traditional water softeners is a ‘once in a decade’ expense, your system needs regular replenishment of salt.
Depending on your hardness removal level, your salt requirement will be different. On average, a household system that can treat 7-10 grain hardness level will need a bag of 40 pound salt per month.
Usually, the cost of a bag of salt ranges between 5$ and 25$, depending on the fineness quality and whether the salt is sodium/potassium based.