Just so there is no confusion, this book was written by the owner of LA Ovenworks and is basically a how-to on constructing an oven from a precast mold, which are of course, sold by the author. This will cost you $2500 right out of the gate for the most basic model. This does not include building the foundation, insulating, plastering or other masonry work, and labor. It's not hard to approach the $10,000 mark with an average size oven.
Having built earth ovens and cooked in them professionally I would highly recommend both Kiko Denzer's book and Building with Cob by Adam Weismann and Katy Bryce. The latter especially if you have no experience working with cob and Kiko's for design ideas. Don't get me wrong, building an earth oven is not easy. But it costs significantly less(especially if you are resourceful in finding reusable materials) and will leave you enough left over to pay some labor and actually buy flour.