From the BusinessWeek article "Why Yahoo's Panama Won't Be Enough" (pointed out by Greg Lindin)
Using data on total search queries, released by comScore, Caris Co. analyst Tim Boyd estimates that Yahoo made on average between 10 cents and 11 cents per search in 2006, bringing in a total of $1.61 billion for the first nine months of the year.It's amazing the Google is twice as efficient at making money off search advertising than anyone else. Better targeting, better advertising model, it makes paid search that much more valuable to the user and therefore allows them to cash in at twice the rate. Keep in mind they also own half the search market.
Google, meanwhile, makes between 19 cents and 21 cents per search. As a result, it made an estimated $4.99 billion during the same period.