My father built a large sturdy shelf unit from reclaimed planks he sourced from left over ammo crates after the war. It can be done cheaply if you are concerned about functionality more than looks. Get some lumber and wood paint. First, you don't care about weight, easy assembly process and shipping costs, so you can use heavier materials, proper metal screws, profiles, brackets, etc. But you do need some tools, like a drill, jigsaw/circular, etc.