Ask HN: Differential Search Engine

If I am casually researching a topic on any of the major search engines Yahoo, Bing, Google, etc works fine and bring up numerous links that are useful. However, when I want to go into more depth in a topic or in an obscure topic (after I have read the top links) I have to go down 2,3,4 or more pages of links to find the hidden gems. I have an idea for a differential search engine that does a search on two different services (say Yahoo and Google) then cancels the most popular or high placed links common to both and displays the remaining links. Does anything like this exist? How hard would that be to do?