Build Your Own Earth Oven is fully illustrated with step-by-step directions, including how to tend the fire, and how to make perfect sourdough hearth loaves in the artisan tradition. The average do-it-yourselfer with a few tools and a scrap pile can build an oven for free, or close to it.
Otherwise, $30 should cover all your materials--less than the price of a fancy "baking stone." Good building soil is often right in your back yard, under your feet. Build the simplest oven in a day! With a bit more time and imagination, you can make a permanent foundation and a fire-breathing dragon-oven or any other shape you can dream up.
Earth ovens are familiar to many that have seen a southwestern "horno" or a European "bee-hive" oven. The idea (pioneered by Egyptian bakers in the second millennium bc!) is simplicity itself: fill the oven with wood, light a fire, and let it burn down to ashes. The dense, 3- to 12-inch-thick earthen walls hold and store the heat of the fire, the baker sweeps the floor clean, and the hot oven walls radiate steady, intense heat for hours.