Thank you to Milan Pohontsch for telling us about this interesting site:

WHAT WAS YOUR ANCESTOR’S PROPERTY WORTH?
Genealogists often find references to money in old deeds and other documents. Even census records frequently recorded estimates of a person’s real estate. The natural question is, “I wonder what that would equal in today’s dollars?” There is a web site that can answer this question. S. Morgan Friedman’s Inflation Calculator can convert a U.S. dollar amount for any year from 1800 through 2015 into the equivalent amount, adjusted for inflation, in any other year of that range. In other words, if you find that your ancestor purchased land for $400 in 1805, the Inflation Calculator (www.westegg.com/inflation) will tell you that the money he spent is equivalent to a purchase of $6371.39 in 2015. (Article by Dick Eastman)