In the context of the decarbonisation of the building sector, this work focuses on the process economics of a carbon capture and utilization alternative for the production of a novel construction material based on magnesium carbonate trihydrate, also known as nesquehonite. This material, after a dehydration-rehydration process, can be conformed into moulds with a significant compressive strength in a very similar mechanism to plasterboard manufacturing. This paper discloses the mass and energy balance of the whole process, where the carbon dioxide is captured from flue gas using aqueous alkaline absorption, and magnesium is sourced from desalination brines. The geographical scope of the economic assessment is the Middle East, specifically Qatar, where desalination and power generation are commonly coupled, and where the huge volume of construction materials imports provide an excellent framework for the development of competitive nesquehonite-based products. In fact, although the process economics show high operating costs, the final product would be economically competitive in the Qatari market at a unit cost around USD 410 per tonne, which is achievable at large scale. The sensitivity analysis shows that both alkali source and the process performance are key aspects of process economics.