This PowerFlex Ready-To-Use Cartridge Sprayer & Lawn Weed Killer Concentrate drops from $11.97 to $5.97 at HomeDepot.com with free in-store pickup. That's 50% off the regular price and the lowest price we could find anywhere. It includes the sprayer and one 4 oz. lawn weed killer cartridge, which makes 1-gallon of weed killer. If you already have the sprayer, you can get a 2-pack of refill cartridges for this same price here. Sales tax is charged in most states.