As I understand it, the cost of CJA is related to the total budgeted row count in Connections for CJA. This includes event datasets and also lookups, profile, and summary datasets.
Using the retention setting, you can determine how much historical data is retained.
If there are events that aren't needed, not ingesting those into the dataset is ideal.
Multiple data views can be created on a single connection, and there's no impact to cost based on data views.
