Although stacked stone looks super expensive, it's rather affordable. Each piece is simply a thin, 1-inch veneer often stocked in a 6x12 size. In order to install as a retaining wall, a contractor first builds the structure out either with pressure-treated plywood or poured concrete. The veneer acts simply as a facade. One thing that definitely drives up cost is mitered corners. This involves hundreds of cuts with a wet saw which takes more time than stacking, staggering and adding mortar.