The backups are made in the cloud, so by definition anything in the backup is stored in the cloud.
If the photos where part of a backup, they will be restored when restoring the backup. There is no fee to restore the backup. Apple will not charge you for it.
Restoring the backup is fairly straight forward process. See here: Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
Note that anything on the iPhone when you restore the backup will get deleted from the device and replaced by whatever is in the backup.
The only backup you will be able to find is the last one that was able to be made before all the storage was used up. Whether that contains the photos you want can only be known once you restore it onto a device.