Databox pricing has four levels: 1) Plan, 2) Data Source Connections, 3) Add-Ons, and  4) Services.
Your subscription cost is based on your plan + the number of data source connections in your account + add-ons and recurring services.
The first three data source connections are free on all plans. Beyond that, you need to pay for each new connection.
As a viable Databox alternative, Whatagraph has all native integrations including BigQuery and Google Sheets available in all pricing plans, so there’s no limit to connecting any data source you have.