Yes, you are paying for both services when you create a second service to make it swappable with the first one. Each instance is billed separately.
In Cloud Service Extended Support, the concept of staging/production slots is not available as it was in Cloud Services (classic). However, you can still achieve a similar workflow by creating two independent cloud services and making them swappable. After deploying and swapping, you can delete the previous instance to save costs. The process to swap in Cloud Services Extended Support is outlined in the documentation here.I hope this helps. Let me know if you still have questions and I will be happy to further assist.
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