Where do you guys buy 50% glyphosate weed killer for a good price online?

I don't. There are two farm stores within a couple miles of each other nearby. I really don't pay much attention to price. They have it, I need it.

I've never seen 50%, I think 40% was the highest I could find. Not hard to use Google to find who has it online for a good price. I bought 2.5 gal years ago, still using that, so no current experience. If there is a Tractor Supply located by the OP, they probably have it. One thing is for sure, if you use a decent amount of it, this is the way to go. It's orders of magnitude cheaper than buying the ready to use and considerably less than even the bottles of Roundup at HD, etc.