Hardware failures in current data centers are common partly due to the higher data scales supported. Data replication is the common approach for improving availability. However, mostly static replication approaches have been proposed, i.e. the number of replicas and their locations are fixed. Moreover, the geographical diversity of data locations has not explicitly been considered. In this paper, we propose a cost-efficient replication scheme across data centers that dynamically adapts the number of replicas employed per partition to the query load, while maintaining availability guarantees in case of failures. Our approach employs a virtual economy that is experimentally proved in a simulated environment to achieve load balancing among data servers at the minimum cost.