Cloud
We have cloud backup for our iPhones. Does this fee not cover my iPad?
iPad Air, iOS 12
There is no fee for using iCloud Backup but if you need more than the free 5GB storage plan, there is a charge for upgrading to larger storage -- see: iCloud storage plans and pricing - Apple Support
The storage plan is linked to your Apple ID, not to a specific devices. You can backup multiple devices to the same iCloud storage plan as long as they are all using the same Apple ID for iCloud.