i buy generic 41% glyphosate from the grain elevator. it was around $52 for a 2.5 gallon jug this april.

buy that. it's probably much more than what you need, but the glyphos won't spoil or go bad if you keep it from freezing. you can use it next year and the year after. if you have your own container, they can pump you some out of a 55 gallon drum and it would cost even less.