The internet sure has a way of doing things like that to people. I mean why buy a product that actually works when you can spend literally hundreds on stuff that only makes them stronger as a whole. Wouldn't make much sense for companies to make a product that actually works if your in to making money.
Avid is also very expensive, but both can be had on Amazon and Ebay is small quantities and both work well.
Obviously if using either of these products plants that are sprayed with it are no good to take to the finish, but you can at least kill your enemy reveg out the plants and take new cuttings and save things.
It's all about using the products the way they were intended, and neither are intended to save a harvest.