Cloud infrastructures employ hybrid storage systems that incorporate various types of devices (flash memory solid-state and hard disk drives). Dealing with such heterogeneity makes the use of data placements strategies necessary. These strategies generally rely on cost modeling techniques. In this paper, we propose a cost model for the storage of database objects in a Cloud infrastructure. Our cost model increments the existing work by including: (1) storage cost, which comprises the occupation, the energy and the endurance costs, (2) the penalty cost that could arise from the SLA (Service Level Agreement) violation, and (3) the migration cost resulting from the object movement between storage systems. We also evaluate the relevance of our model and its usability throughout examples.