The Funnel API, BigQuery and S3/Redshift integrations contain some metrics prefixed with common- and other that start with the name of a specific ad platform.
The common- metrics in general reflect the Funnel view of what is the most common interpretation of that metric across platforms. For "cost" that is usually the total cost/spend for the advertiser regardless of this is based on impressions, clicks or conversions of some type. In most cases you should be able to work only with common-cost as a way of aggregating and comparing cost across all ad platforms.
When is common-cost different from adwords-cost?
But if you sum those rows together (in your own Data Warehouse, or in Funnel using some other Dimension, the totals for those columns would be 190 for common-cost, 90 for facebook-cost and 100 for adwords-cost.
I'm missing the cost for a specific ad platform
Going forward Funnel aims to provide both the common-cost and ad platform specific cost metrics. In some cases older integrations may not have them yet. In most cases you should be able to work with common-cost at the right level of detail (see above), and otherwise let us know if there is one you are missing.