Voltage Source Converters (VSC) have been widely utilized to provide instantaneous reactive power support to power systems, an application referred to as static synchronous compensator (StatCom). Integration of energy storage (ES) into a StatCom makes it possible for the StatCom to provide a certain amount of active power as well as reactive power support. The possible benefit of the additional active power of a StatCom can be power oscillation damping capability, mitigation of phase-jump related disturbances, etc. Direct connection of an ES device to the dc link of the VSC incurs unnecessarily high voltage rating of the VSC due to the considerable voltage swing associated with the ES device. A dual thyristor converter topology has been proposed as the interface between the ES and the dc link of the VSC. In this paper, a cost estimation for systems with the proposed interface topology is presented regarding three types of ES: capacitors, supercapacitors, and batteries. The study shows potential cost savings by utilization of the proposed interface topology. In addition, a cost comparison between different types of ES is presented, providing a guideline for the choice of ES in this kind of applications.