Publicis/Denuo recently completed a study and found that the cost of executing online campaigns (excluding creative development) represented approximately 15-20% of the media spend on average, compared to offline execution costs on the order of 2-3% of media spend. That is an astounding cost differential, if you think about it, and one of the major reasons that only 3-4% of brand dollars have migrated to the Internet to date (compared to ~15% for direct response).

Has anyone seen this study? Src: AdExchanger