You will notice a Traffic Cost number listed for domains when using Organic Positions or Advertising Positions reports. Traffic Cost is how much an advertiser would have to spend on average per month in Google AdWords to rank for all of the keywords listed in the report. This number is provided to give you a baseline estimation of how valuable a domain’s keyword portfolio is. If you are unable to organically outrank your competitors and prefer to target keywords with PPC, this metric will be valuable when planning your campaign.
This metric is gathered through a proprietary method that takes multiple values into consideration including CPC, volume, competition level, and more.