The key to a successful business is good margins, the difference between what you buy stuff for and what you sell it for. So when what you're selling costs you nothing to buy, and it retails for $50 or $100, you're in good shape.
Such is the case with Justin Gignac's New York City Garbage project, in which the artist/entrepreneur gathers trash found on the streets of Manhattan, packages it into cubes, and sells it for the price of an expensive bottle of wine. In the process, he manages to simultaneously indict and celebrate the culture of consumerism.
Turns out people are happy to pay for nicely packaged garbage - Gignac has sold over 1,200 units so far.