I'm currently in the middle of the process of linking my Google analytics data to Big Query and the following note caught my attention when selecting the view to pick.
If this is the first time that you have linked this view, then data will be backfilled for the smaller of 13 months or 10 billion hits.
Its a little unclear to me whether this 13 months of data will have costs in importing once I linked to BigQuery.
The process itself doesn't have a price component for back filling, but the storage it will occupy in BigQuery adds to your storage costs.
If you don't want old data, make sure you archive/remove/delete it.