That's because poured concrete tends to be more expensive than cinder blocks. Technically, what we know today as cinder blocks are actually called "concrete masonry units," or CMUs. Real cinder blocks are made with cinders from fly ash (a type of coal ash); in most modern cases, the term "cinder" refers to concrete. (See what the average lifespan is of cinder blocks.) Meanwhile, the price range of poured concrete is greater, starting at around $8 and going to $20, or about 25% more than cinder blocks.