It is been considered that the cloud computing solutions reduces the cost of computing resources as far as organization is concerned. However, a recent white paper from ISACA indicates that the true cost of cloud computing may be higher than earlier thought values. In the white paper titled .Calculating Cloud ROI : From the Customer Perspective. ISACA provides a detailed framework on how the cost of cloud computing operations shall be assessed for a better understanding towards calculating the ROI of cloud computing

It explains .The acceptance at lightning speed may be attributed to its appeal as a low cost-of-entry and rapid return on investment (ROI) solution. This view, however, may only consider the immediate costs of contracting and migrating to the cloud and fails to consider the long-term costs of operating in the cloud and, worse, the hidden costs that could minimize the expected return. To add to the complexity, cloud computing encompasses a variety of service delivery and deployment models, ranging from public and community to hybrid and private clouds. These services are offered by a variety of providers, each with different solutions and pricing models.

The estimated costs section of the white paper gives some interesting insights of the hidden costs, which should be considered for calculating the ROI.

• Cost of rebuilding the infrastructure back in your data centre for business / regulatory reasons.
• Flexibility of the systems
• Lock-in requirements of the contract and possible unsatisfactory service
• Loss of internal IT Skills 
• Risk management costs

It is an interesting white paper, if you are considering cloud based solutions for your business. You can download the article from here