Lowes: project was just shy of $100. The pebbles have a diameter of 5 feet and are only about 3″ deep. The stones have an outer diameter of 4 feet (might want to go larger). It’s 4 rows high. 52 stones total and 4 cubic feet of sandstone pebbles. Provide air holes between the stones for oxygen. Step 3 is just removing the grass, and digging a shallow hole about 3″ deep.