You can always bring down cloud computing cost by opting for public cloud. However, you must remember that public cloud, unlike private cloud, does not keep different users on different cloud resources. Some users could be using shared resources. For some business operations, public or shared cloud services are quite useful, but not for all.
Once you figure out which of them is a better solution, it becomes essential to check if the cloud platform supports multi-tenant operations. Also, you must check if the cloud service provider keeps your business element isolated through server instances located across geographic locations.