Interesting, from NZ.
www.fishing.net.nz
" ............a lot of salters on the net get theirs from a pool-supply shop. This is incredibly cheap: a bit over $10 for 25kg "
Wondering about water softener salt. Its pretty cheap too.

Salting Baits - The Fishing Website
Salting your bait is a great solution to some of the drawbacks of fresh bait, such as mushiness, blood, slime and restricted shelf life. Salted baits are tougher, so more resilient during casts or when pickers are about. They also don’t need freezing or refrigerating, so can sit on a shelf...
" ............a lot of salters on the net get theirs from a pool-supply shop. This is incredibly cheap: a bit over $10 for 25kg "
Wondering about water softener salt. Its pretty cheap too.