You want to know a real shocker?
We buy foil about once every 5 years. We get the huge industrial thing from Costco. Last time we bought some it was about $15 for it. I hadn't looked at the price of foil since.
Flash forward to a couple months ago and it was about $30!
Anyone who tells you there isn't inflation has been hiding under a rock and not buying thing.
The short answer to your question: The dollar has been losing value over the past several years as the Federal Reserve 'quantitatively eases' our currency into oblivion.
As the value of a currency goes down, purchasing power goes down. One of the most blatant things that rise and fall proportionately are metals.
hence why people are stealing wiring and pipes from homes, man hole covers ect. ect.
It's also why gold has gone from $500 an ounce to $1700 an ounce in about 5 years. heck silver went from $10 to $30 an ounce in about 5 years too. Copper, Nickle ect. ect.
The metal value of a penny and a nickle are now worth more than the face value of the coin.
Inflation is the hidden tax.