My LFS sells RO/DI water for 70 cents/gallon, but the local grocery and all local Walmarts have RO water outlets at 30 cents/gallon. The catch there is the LFS sells it with the de-ionization step so it's specifically for SWF. I have been taking the cheap route, personally, for over a year. Though on Thursday I finally bought an RO/DI unit and am already putting it to great use.