Earth is abundant.
Earth is everywhere.
And this technique of building earthen furniture, called cob, a combination of five ingredients: clay, sand, straw, water & human energy.
All the clay came from this very land and to make the perfect mix I added a bit of sand & straw.
Really the most "costly" factor was time. But, as we plan to spend many hours sitting on this bench for years to come ... I think it was worth the effort.
I hoped to write a whole tutorial on how to build with cob, but, the truth is I am learning as I go and experimenting along the way. At this time I am in no position to give guidance on the subject of natural building besides the inspiration to give it a try.
As one wise builder once said "the mountains are made of clay and stone, and they do not dissapear after a rain".