I recently purchased five 40' bags from the site below. http://purearagonite.com/home.html
It costs $11.95 per 40' bag. If you buy 4 or more bags you get 1 bag free. So the aragonite sand cost me $47.80 for 200'. The shipping cost about $55 so the total to have it shipped to Chicago was about $102 for 200 lbs.
Eddie G
If you need a ton of it, do what Eddie G did, but if not, buy it from a LFS. You can order a 40 or 50 pound bag on the internet, but shipping will be an arm and a leg.