Inflation is generally around 3% a year, which means over a decade prices will rise more than 30% (each year’s 3% is on the previous year’s increase, so the inflation for ten years is more than 30%). Twenty years would bring well over 60% price hike. That’s why burying your savings in the back yard isn’t a good idea (and is why the Federal Reserve engineers a steady inflation, to discourage "hoarding" and encourage investing)

Also a society changes demand changes so the prices of some things drop, while the proce of others rise. DVD players seem to get less expensive each year, as well as CD players. The price of phonograph players dropped to almost nothing in the mid 80’s and is now rising as they become more and more museum pieces.