Yes, in the case you described, the Starter plan would be used for the preview environments. If all 10 PR environments ran for a full month, you are correct, that would be $70. However, we only charge for the amount of time the service exists, down to the second. So if your services only exist for a day you would only be charged for that time. You could also set the previewsExpireAfterDays to have preview environments deleted after a set number of days.