"Food grade" vinegar, 9 or 10% pickling vinegar is the ideal strength for killing weeds. You may go to the feed store and spend $36 for four gallons of "Nature's Guide" high priced (and not food grade) vinegar like you find at
Marshall Grain and other feed stores, or you can buy environmentally healthy food vinegar for $10 at [img=http://www.davidsfoods.com/]David's Supermarket[/img] and other grocery stores. Most city grocery stores don't seem to have it, you need to go into the countryside. All of this vinegar is made by a spinoff of Fleischmanns down in Houston.
Don't worry about the poor picklers not getting their vinegar. The grocery stores will order more. And with high volume comes lower prices (I haven't seen a run on any of the ingredients that go into vinegar, it's not like the price of a barrel of oil.)