interesting, you gave me something to test. Thanks for the insightCost is certainly a good reason for choosing a mix, but I'm not sure that mixes that take less solids will cost less. The difference is some have less water in the solid crystals than do others.
Anhydrous salt mixes (those with less water) are more often the costlier ones, not the cheaper ones. It take extra energy and processing steps to remove water from the calcium and magnesium salts put into salt mixes, so making them more compact might make them more expensive too.