need advice regarding salt water marine aquarium

hi, my wife wanted a salt water fish tank....  I bought a 90 gallon tank.......    I was about to order the salt online and then was surpreised when it was going to be about 1,800 baht to buy enough salt for 90 gallon....    I remember driving somewhere only about an hour outside of bangkok where they had all of these sea salt farms.  ,,,,,,,,,,  I can buy a huge bag of that for like 300 baht.   

SO my question is 1. is it the same stuff minus  pretty retail packaging?     2. if its not the same,,, can i still use it and the fish be healthy,,,,,, i mean it comes from the sea?

really appreciate some advice