If you aren't looking to buy more than 50lbs from a farmer thenyou can save alot of money over the grocery store at a bulk store.. Around here is roughly 10x cheaper that way.. I ferment rum with it, I get it for 91 cents/kg.. Most bulk stores carry black-strap, and fancy molasses in unsulphured form..
Also, if you want to strip the micros from the sugar portion to keep your system less sticky and attractive to bugs, you can mix molasses with warm water, and let it settle for a day or two.. The liquid portion will contain the vast amount of sugars, and the silt on the bottom will contain most of the rest.. I do that when I ferment light rum washes, except I'm after the liquid portion..