Here is a great idea for a cheap and easy compost bin, courtesy of the blog Homegrown Evolution: use some slightly modified worn-out old tires stacked on top of each other. I can see that you might want to cut some holes through the tired for better aeration, but the modularity of the design and the easy availability of scads of tires make this a pretty cool idea.

Take a look. We could make gazillions of these and give ’em away!