This paper carried out the thermodynamic and economic optimizations of a subcritical \ORC\ (Organic Rankine Cycle) using a pure or a zeotropic mixture working fluid. Two pure organic compounds, i.e. n-pentane and R245fa, and their mixtures with various concentrations were used as \ORC\ working fluid for this study. Two optimizations, i.e. exergy efficiency maximization and \LCOE\ (Levelized Cost of Electricity) minimization, were performed to find out the optimum operating conditions of the system and to determine the best working fluid from the studied media. Hot water at temperature of 150 °C and pressure of 5 bars was used to simulate the heat source medium. Whereas, cooling water at temperature of 20 °C was considered to be the heat sink medium. The mass flow rate of heat source is fixed at 50 kg/s for the optimizations. According to the results, the n-pentane-based \ORC\ showed the highest maximized exergy efficiency (53.2%) and the lowest minimized \LCOE\ (0.0863 /kWh). Regarding \ORCs\ using zeotropic working fluids, 0.05 and 0.1 \R245fa\ mass fraction mixtures present the comparable economic features and thermodynamic performances to the system using n-pentane at minimum LCOE. The \ORC\ using \R245fa\ represents the least profitable system.