while the price of autos went down in the 1910's and 20's there was a recorded DEPRESSION in 1921-23

"To be sure, the 1920–1921 depression was painful. The unemployment rate peaked at 11.7 percent in 1921. But it had dropped to 6.7 percent by the following year, and was down to 2.4 percent by 1923. After the depression the United States proceeded to enjoy the “Roaring Twenties,” arguably the most prosperous decade in the country’s history. Some of this prosperity was illusory—itself the result of subsequent Fed inflation—but nonetheless the 1920–1921 depression “purged the rottenness out of the system” and provided a solid framework for sustainable growth.
As we know, things turned out decidedly differently in the 1930s. Despite the easy fiscal and monetary policies of the Hoover administration and the Federal Reserve—which today’s experts say are necessary to avoid the “mistakes of the Great Depression”—the unemployment rate kept going higher and higher, averaging an astounding 25 percent in 1933. And of course, after the “great contraction” the U.S. proceeded to stagnate in the Great Depression of the 1930s, which was easily the least prosperous decade in the country’s history.
The conclusion seems obvious to anyone whose mind is not firmly locked into the Keynesian or monetarist framework: The free market works. Even in the face of massive shocks requiring large structural adjustments, the best thing the government can do is cut its own budget and return more resources to the private sector. For its part, the Federal Reserve doesn’t help matters by flooding the shell-shocked credit markets with green pieces of paper. Prices can adjust to clear labor and other markets soon enough, in light of the new fundamentals, if only the politicians and central bankers would get out of the way."
http://www.fee.org/the_freeman/detail/the-depression-youve-never-heard-…