Each publisher determines its own CPI rate (Cost Per Impression). In other words, each time your visual is displayed based on your instructions with no segment or targeting limit.
As a reference, the CPI will be displayed on your performance reports.
We also ask you to specify a campaign budget. We will never go beyond this budget, but since we cannot control the supply and demand, if we do not have enough available impressions, we will only charge you for the actual number of impressions delivered.
We do not charge differently for each variable, segment or keyword. We use a unique rate.