In my neck of the woods I can only find 2.5 gallon bottles of glyphosate at Farm & Fleet. Here's a list of other places I've checked that do not carry a generic:
True Value Hardware Stores
What I buy from Farm & Fleet is Crop Smart (41% glyphosate). It's on sale several times a year for 34.99 or full price of 39.99
It takes ~2-weeks like everybody else is reporting. I mix it at a heavier concentrate than recommended using 5-6 oz. per gallon. My weeds die somewhere in the range of 10-days at that rate w/o a second application necessary for tough weeds like purslane.