Custom Cut for Stair Tread

I need a custom-shaped cutout on the back of a 3-inch thick wooden stair tread to accommodate a metal plate. only need 5/16 inch deep . its white oak so probably do in increments of 1/8" Requirements:... (Budget: $30 - $250 USD, Jobs: 3D Modelling, 3D Rendering, CAD/CAM, Carpentry, Furniture Design, Graphic Design)