The economic feasibility of FO, crystallization and RO hybrid process was analysed on the view of specific water cost. Selecting appropriate draw solutes for the hybrid process, cost evaluation model was developed considering capital and operating cost. To solve MINLP problem efficiently, the problem is divided into FO, RO and crystallization. Each specific water production cost was calculated in FO and RO individually, and the costs of them are fitted as functions of recoveries. Then, the overall specific water cost can be calculated as a function of recoveries of FO and RO. Then the MINLP problem becomes an ordinary NLP problem. Considering three different FO membrane, the minimum specific water cost is 0.5727 $/m3 when mLbL-10 membrane as FO process and disodium phosphate as draw solute. Comparing 0.6452 $/m3 of conventional RO process, this hybrid process is competitive and can be an alternative to conventional RO process.