Question

after the civil war the cost of living decreased because

Answer 1

a: sanitation and medical care improved
b: consumers wanted imported goods.
c: technology made manufacturing more efficient

Answer 2

How far after the Civil War? In the immediate aftermath of the Civil War, the cost of living in the South climbed enormously, due to the massive destruction of infrastructure, not to mention the death and disruption. In the North it increased because of the death and disruption, as well as with the collapse of government demand immediately after Appomattox. The culmination was probably the Panic of 1873.

However, if you mean later -- from the 1870s to about 1890 -- there was indeed a decrease in the cost of living due to rapid Northern industrialization (reducing the cost of manufacture of goods) and the explosion of rail transport, which significantly reduced the cost of goods grown or manufactured far from their point of consumption.