Sorry for that as I often forget that a lot of people don't use a lot of brine and therefore don't use much salt water for them.
Most of the people I am directly connected with in the seahorse hobby are raising brine shrimp to larger sizes up to adult, and that's where the savings come in. Salt prices here in Canada are significantly higher than in the US I believe, most likely due to shipping costs.
For me, I have a minimum of four 26g containers of various growth stages of artemia, and a minimum of 5g of rotifers, and, at any given point, between 20 and 150g of nannochloropsis under culture, so it's a big savings for me.
As for anything lacking in the culture water, I've been doing this large scale for well over a decade and there has been no problem whatsoever with raising them.
When you think of it, the reef salt mix makes salt water that is nowhere near the makeup of the salt water in the Great Salt Lake, and other bodies of water where artemia are found.
It is not even needed for the nannochloropsis as the f/2 fertilizer supplies all that it needs.