This is the third in a series of papers on alternative cycle evaluation. Part I described the evaluation methodology. Part II described the down-selection process where the most promising of the nine alternative cycles was determined. The Cu-Cl cycle was selected for further development because it alone meets the four criteria used. The current results indicate that the cycle is chemically viable, feasible with respect to engineering, energy-efficient, and capable of meeting DOE's timeline for an Integrated Laboratory Scale (ILS) demonstration. All of the reactions have been proven and the remaining technical challenges should be met with current technologies. The maximum temperature requirement is around 550 degrees C (823 K), which can be obtained with a variety of heat sources. The lower temperature should mitigate the demands on the materials of construction. This paper, Part III, describes the procedure used to develop the Cu-Cl cycle beyond the relatively simple Level 3 efficiency calculation completed by the universities. The optimization process consisted of (i) updating the thermodynamic database used in the Aspen Plus' simulation, (ii) developing a robust flowsheet and optimizing the energy usage therein, (iii) designing a conceptual process incorporating the Aspen Plus' mass and energy flows, and then (iv) estimating the hydrogen production costs. The results presented here are preliminary because further optimization is ongoing. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.