Emerging inter-datacenter applications involving data transferred, processed, and analyzed at multiple datacenters, such as virtual machine migrations, real-time data backup, remote desktop, and virtual datacenters, can be modeled as virtual network requests that share computing and spectrum resources of a common substrate physical inter-datacenter network. Recent advances make elastic optical networks an ideal candidate for meeting the dynamic and heterogeneous connection demands between datacenters. In this paper, we address the static (offline) version of the virtual network mapping problem in elastic optical networks equipped with sliceable bandwidth variable transponders. The objective is to minimize the total transponder cost in the network. An Integer Linear Programming formulation is presented, lower bounds are derived, and six heuristics are proposed and compared. Simulation results are presented to show the effectiveness of the proposed approaches.