1. A method of valuing services for search engine optimization (SEO) of a campaign term, the method comprising: retrieving search query volume information for the campaign term; determining a first probability that a search query for the campaign term will result in a referral from a search engine; determining a plurality of second probabilities, wherein the second probabilities are each associated with one or more particular positions in a search engine results page; generating an organic price for each of the one of more particular positions based on the search query volume information, the first probability, a second probability for a particular position, and a monetary value for the particular position; and generating a value of the SEO services for the campaign term based on the organic prices for the one of more particular positions; wherein determining the first probability, determining the plurality of second probabilities, generating the organic price, and generating the value of the SEO services are performed, at least in part, by one or more computing devices.