Littlesilvermax and a few other sellers carry pharmaceutical grade magnesium chloride hexahydrate which generally comes to $4 or $5 a pound after shipping so its not too bad cost wise. However Lonnie discovered that at Atco Wholesale in town we can buy regular non-pharmaceutical grade for less than $1 a pound. The product is call Absolute Zero Melt Down and sells for under $30 for a 50 pound bag. He has been using it for about 2 years I guess and I've now been using it for a year as well without any apparent side effects. So weigh the options, the slight risk might not be worth the cost savings but that is for you to decide.
I had a thread about it last year
http://canreef.com/vbulletin/showthr...=absolute+melt
I believe the rate you mix it with Magnesium Sulfate is either 10:1 by volume or 7.1:1 by weight.
The other ice melting product available which Randy talks about in that article is quite difficult to get in Canada.