If you look at the inflation-adjusted Dow, you can see it's way cheaper when compared with 2007, not to mention 2000. The market is on the level of 2002 or 2003 when measured by monetary inflation. Not exceptionally cheap, but not exorbitantly expensive, either.
Monetary inflation is defined as the growth of the MZM (Money Zero Maturity) aggregate. It is the sum of money in the U.S. economy, which may be theoretically available in the liquid form within 24 hours. Just cash, demand deposits, savings accounts, money-market funds. No time deposits.
Consumer Price Index, the more common measure of inflation, is of no use here. The CPI measures the price of the basket of goods or services of final consumption. Equities are neither goods nor services. They are investments; therefore CPI cannot be used.