One dollar, apparently. That's the philosophy behind the Million Dollar Homepage, a site launched by 21-year old Alex Tew, a college student in the UK who is trying to cover the cost of his studies.
You can buy ad space on his page for a dollar per pixel. he has divided up the page into blocks of 100 pixels (10 by 10 squares) and he's selling them off alone or in groups. There are live stats at the top of the page to track his progress.
So, does advertising on his site actually pay off? Apparently, as evidenced on his page of press coverage. One company, Littleredbear.com, claims it saw a 150% spike in traffic since it bought a block of pixels on Alex's site three weeks ago.
Just goes to show: all you need to make money on the Internet is one really good idea.