Cost of model calculation depends on its parameters, number of sessions and source on information and it's billed by Google accordingly to BigQuery pricing plans.
You can check volume of data processed for each model on “History” tab.
Also please note that data is also processed to show results of searches on “Learn more” tab. You can check volume of data processed to execute each search query in notification message that appears in the lower left corner of the screen.
Examples of calculations
|Size of data source tables
|Volume of processed data
|OWOX BI Pipeline
|BigQuery Export for Google Analytics