I've done it. Cost effective? Sure, I suppose if the wood is free and your time is worth nothing. It was a fun project once, but I don't know if I would go through the trouble again. I took advantage of a stack of free wood, a free rusted out barrel, and a huge pile of brush that needed burned at my grand parents place. The charcoal was good, but no better than lump I had bought at the store. It was also a messy PITA to remove from the drum and bag.
I'm a big fan of prebagged charcoal on sale 😀