5. The method of claim 2 wherein the financial benefit is generated from purchases of items within a category during a session initiated with the selection of an advertisement for the keyword and the determining of the bid amount includes accumulating combinations for each category of the financial benefit for that category and the category-specific advertising expense factor for that category and normalizing the accumulated combinations by number of sessions resulting in the financial benefit.
5. The method of claim 2 wherein the financial benefit is generated from purchases of items within a category during a session initiated with the selection of an advertisement for the keyword and the determining of the bid amount includes accumulating combinations for each category of the financial benefit for that category and the category-specific advertising expense factor for that category and normalizing the accumulated combinations by number of sessions resulting in the financial benefit. 6. The method of claim 5 wherein the determining of the bid amount includes multiplying the normalized accumulated combinations by a forecast conversion rate.