Making sea salt from saltwater is very easy, although quite time consuming. It's not necessarily cost effective, but it's a lot of fun and a rewarding learning experience.
How much salt are you going to get? I read on one website
that the rule of thumb is 5 gallons of seawater to 4 cups of salt, which would mean a 5% salt solution. I did 4 gallon batches, and got between 2.5 and 4 cups per batch, which is a bit of a lower yield. However, my small batch of 2 quarts gave me 1 full cup of salt, which is much higher. So it all depends on the original saltiness of the seawater and the method used to evaporate it, and how careful you are not to lose any salt to the floor in the process (I speak from experience—I lost more than I'd like through careless pouring).
Overall, I processed 16.5 gallons of seawater, and I ended up with over 9 cups of salt. This is a total of about a 3.5% yield by volume of salt from saltwater, but your mileage may vary. I documented my own experience on my blog
Let's get started!