Artist Christopher "CK" Wilde chose an expensive medium for his art: money.
From the website:
Wilde painstakingly cuts various shapes out of paper money from around the world to form collages with economic and political undertones and overlays. The relationship between art and commerce is another theme that cannot be avoided when an artist cuts and pastes with money. Wilde bases a lot of his works on found images that he develops into his own compositions, which he will lay down on museum board before skillfully applying his umpteen bits of currency so that they abut in order to keep to the ideal of an even surface. The resulting puzzle is then sealed with wax. A tidy alternative to keeping it under the mattress.
This one above is titled "Against the Common Good". Link | Gallery (via Boing Boing)