Initially I was thinking this is a bad idea but then I looked the content of euro coins ands they are made from at least 75% copper, and depending on banknote there nickel and zinc in different percentage.
Now, copper has lower melting point than stainless steel but I still consider it a very good and cheap material alternative for bitcoin metal backup.
Note that some countries may be using different and lower percentage of copper in their banknotes.
Imagine one crazy thing... using silver coins instead of euro coins to increase value 

I am not following this account, but this is certainly trending in twitter for bitcoin related stuff