Oh wow, you just described the exact goal I have for my life. I plan on buying some land after working and traveling for many years. Need at least 5k if I want to buy land in the desert, and over 20k for anything where there's fertile soil. I highly recommend WWOOF or Helpx. You'll learn everything you need to know about growing your own food. I don't believe it's possible to build a shelter and garden for yourself in any ol' forest because every acre of land is owned by someone, whether it's an individual or the government. The cheaper the land the shittier soil you're going to have. Maybe you could build yourself a greenhouse powered by solar energy? I haven't looked into it so I don't know how that works, but you could buy cheap land in Texas and build yourself a greenhouse. There was a point where I considered joining an eco village but the nice ones I saw were interested in people that could offer their community some kind of service, like someone that was skilled in growing plants, knew how to build earthen homes, artist, etc. I have literally nothing to offer so I didn't bother applying. And really, the idea of living secluded is more appealing to me. Here's a couple of websites. This one is all communes and intentional communities. http://www.ic.org/directory/communes/ and this one you can browse to get an idea of land prices http://www.landwatch.com/

Here's a youtube channel for inspiration. https://www.youtube.com/user/kirstendirksen