It's surprisingly cheap when you compare it to television advertising, but pretty expensive when you consider the high amount of clutter and how little attention people actually pay. This interesting video, from the folks at GOOD Magazine, shows just how much advertisers are paying to bombard New Yorkers with out-of-home advertising.
Hat top to YesButNoButYes, where I first saw this clip. And another to PSFK for their ongoing exploration of the urban spam phenomenon.