Today I went through my latest lot of mixed LEGO pieces. There were some interesting minifigures already worth the money, but when I got to the bottom of the pile I hit the literal (LEGO) gold. There were many of the small gold goins used in various old Pirates sets. As such a small pieces they often are the first pieces to get lost. Also as they are painted with chore gold paint that tends to chip away over decades.
These coins, 12 in total, were in nearly perfect condition. For a such small piece they cost quite a lot compared to their weight. In good condition you need to pay around 1 euro per piece. While not a lot of money it is still good money for something so small. Almost, but not quite as expensive as real gold, which still costs around 3,5 times more.
But there are other old and small pieces that are even harder to come by. For example the small feather plume, especially in black, is over 7 times more expensive than gold! I have yet to come across such treasure although in my previous lot there were 3 blue ones that are half the price of the black ones.