I want to make concrete planters and sell them.
I need to make a mold, I think the easiest way would be to use fiberglass on a plug. But I can't figure out how to make a plug easily and for cheap. I considered that green foam you get from craft stores, using thick blocks to make layers of the planter shape, but I don't know how well it would work. There's also wood, but I don't have a wood lathe to make perfectly concentric parts.

anyone have any ideas on materials or methods?