My water softener uses 120 pounds of salt per month. It's cheap but I expect the biggest part of the cost is shipping it from wherever it came from to a store near me.
We have plenty of water here and will likely have too much after El Nino winds down, but the coastal regions of Florida have horrible water and a lot of salt water intrusion. We already have one desal plant that supplies 25 million gallons a day to the Tampa Bay area but may be looking at more before long too, particularly since rising sea levels are gonna cause even more salt water intrusion.
Dams and aqueducts don't work all that well here since there is so little in the way of elevation changes.

Good coffee, good weed, and time on my hands...