A method for providing a virtual cloud service at the lowest actual cost can begin with an optimal transaction handler of a federated virtual service cloud maintaining a virtual resource pool of transactional units. Each transactional unit can represent a service application deployed to a cloud service provided by a cloud service provider having a usage-based service cost model that allows transactional units to be placed in an inactive state to suspend its operating expense. Operational metrics data for the cloud service providers can be continuously captured. In response to a service request, the transactional unit that meets fulfillment requirements of the service request and incurs a lowest actual cost can be determined based upon cost factors derived from the operational metrics data, the usage-based service cost model, and a current usage state of the virtual resource pool. The received service request can be routed to the determined transactional unit.