The need to reduce energy consumption in seawater Reverse Osmosis (RO) process has pushed research towards the development of new hybrid systems in which, for example, other membrane processes can be used to pretreat seawater. Electrodialysis (ED) and Reverse Electrodialysis (RED) can act as a pre-desalting step before seawater enters the RO unit, thus leading to an important energy saving in RO. In this work, two coupled models are proposed for the RED-RO and ED-RO systems. Each process model was validated. Then a sensitivity analysis was performed to assess the effect of the integration on the overall process cost saving. The analysis was performed by changing ED or RED voltage and RO pressure and considering eight different cost scenarios. The performance of the hybrid system was compared with the stand-alone seawater RO process. Competitive scenarios were found especially for the RED-RO case, by optimizing the pre-desalting extent, with significant cost saving and promising potentials for future industrial implementation.