I simply put 3 pallets together for a simple compost bin. You can get pallets free of charge at most lumber yards or "big box" stores. I put one on the rear and fasten 1 on each side with long screws or nails then put a piece of 1x4 across the front at the top to keep it from spreading. I have 2 of those right now----1 for new compost and 1 for stuff that is done but not quite needed just yet. Each bin is approximately 4 ft. tall by 3 1/2 ft. wide and deep.

When they finally fall apart after a few years, simply get more pallets and make more for free.