Stopped instances are not billed for RAM or vCPU. Disk storage for stopped virtual machines is billed at the same rate as active virtual machines. If you wish to not pay for that instance, you are free to take a backup of the instance and make a template out of that backup for future use. Backup/Image storage, which is SATA3 HDD, is billed at a lower rate compared to "primary" storage, which is SSD.