At the Scripps institute of oceanography you can actually fill up with ocean water free!.When I lived in CA and was planning a large build, I looked into having water delivered. The guy would take his boat several miles off the coast pump it onto the boat through a pre filter then onto his truck to deliver it and pump it right into the tank. When factoring the cost of salt and time for the rodi, it became more worthwhile. I don’t know if it’s still as good of a deal but might be worth it for the first fill up.
I have a 600 gallon in bed water container I’m planning on using to fill her up when the time comes