With orders of $25 or more, Amazon offers Prime members the Kirkland Signature Pure Sea Salt 30-oz. Bottle for $2.79 with free shipping. (Non-members can spend $49 to qualify for free shipping.) That's about a buck below what you'd pay at a warehouse store locally.
Note: This item is part of Amazon's "add-on program" and can only be purchased with an order of $25 or more.