I used it once, last fall on some pastures. It did make the grass greener, I'll give it that much. You could tell the sprayed areas pretty easy. But it was late enough in the season that we didn't get much growth after I sprayed. I will probably give it another try this spring. One concern I have is with the sodium though. Sodium doesn't do good things for the soil structure, it breaks down the crumbly texture, in high enough concentrations. Whether this stuff has enough of it in it to damage the soil after some amount of sprays, I don't know. Like I say, just a concern I have for now.
I'm thinking it was less than $18 an acre for the material, more like $3. Unless you are talking about something other than the granulated sea salt from that outfit in Arkansas.