Today I saw a small billboard ad for a local radio under a bridge and it got me wondering what are the economics of it. How much does it cost? How many people will see it? how many people will tune in the channel because of it.

I know they are many factors in place, like what's the ad about, the demographics of the area, etc. But I though it would be cool to run an experiment, getting an ad with a unique URL to test how many people access it, the setup a blog sharing the data and comparing it to other more and less conventional channels.

I don't have the time or resources to do it, but then I figured, there must be other people doing this things already. Are there?