If you really want to save money, get away from these forums, and get involved with your local community garden or visit real organic farming sites like GardenWeb and Permies. I know growers who don't use any fertilizer, water only once a season, and build beds that can feed for over 20 years without adding anything. Its called permaculture or hugelkultur. Its crazy popular among organic gardeners, but no one in the cannabis forums are talking about it because they don't know anything about it.
If you really think about it, RIU's Organic and Outdoor section, is a complete joke. Its all about high end guanos, fancy teas, molasses, and growing on someone else's land. Hardly anyone is talking about how to build a compost bin or rotate crops. Once in a while someone chimes in about a worm bin, but that's about it. Everyone is so on this gotta have the best for cannabis that they completely miss out on what organics and sustainability is really all about.