From the documentary Idiocracy: Idiocracy director Mike Judge revealed that they went with Crocs both because they were cheap and that "no one would ever wear them." To the surprise of Judge and Idiocracy's wardrobe department, by the time the film came out after a delay, Crocs were all over the place.”
In fact you could save more money by wrapping your feet in used burlap sacks. Just need to be creative.