Here's what I found on Wikipedia about Dead Sea chemistry:
"These results show that the composition of the salt, as anhydrous chlorides on a weight percentage basis, was calcium chloride (CaCl2) 14.4%, potassium chloride (KCl) 4.4%, magnesium chloride (MgCl2) 50.8% and sodium chloride (NaCl) 30.4%. In comparison, the salt in the water of most oceans and seas is approximately 85% sodium chloride. The concentration of sulfate ions (SO42−) is very low, and the concentration of bromide ions (Br−) is the highest of all waters on Earth."
So it's mostly just a mix of chlorides of sodium, magnesium, calcium with a less significant amount of potassium chloride and by the looks of it bromides of at least some of these ions too but the article doesn't really say what the bromide levels are just that they're higher than in any other natural waters. I'm a bit surprised to see sulphates are so low. I expected to see some sulphates of calcium, magnesium and sodium in there as well but I guess not so much. If the dead sea salt is expensive you could sort of mimic it by using a mixture of sodium chloride with de-icing salt or dust control mixture which are usually either calcium chloride or a mixture of calcium and magnesium chlorides. You wouldn't likely get any or much KCl but that's just a minor component of dead sea salt anyways so it probably wouldn't make much difference.
I don't lnow much about salt water systems. What kind of concentrations of chlorides do you run in them? Personally, I wouldn't want to use those systems if the [Cl-] is very high. Chlorides are very mobile and persistant in the environment and contaminate groundwater very easily.