This is the simplest bench that I have been able to come across that is both eco friendly as well as sturdy and very quick to build and use.
There really should not be to much need for written instructions on this one but I will include two photographs just in case..
You can go all out and rough cut you board as well, however driving by a dumpster at a construction site would do the trick if you want to spend no money whatsoever. Just be sure to find someone who speaks English if your in the USA and ask for permission first.