The cost-effective analysis (CEA) of hydrokinetic farms is typically based on simplistic assumptions regarding the performance and cost structure of hydrokinetic energy converters (HECs) and, in consequence, may lead to illinformed decision-making. In this work, a novel approach to selecting the most appropriate combination of HEC and site within a coastal area is developed, with the accurate computation of the CEA parameters as the cornerstone. The approach, which is illustrated through a case study in the Shannon Estuary (W Ireland), encompasses four models, namely: (i) HEC-site selection model, (ii) energy production model, (iii) CAPEX model, and (iv) OPEX model. By avoiding simplistic assumptions, the proposed approach improves on current procedures and enables developers to accurately compute any cost-effective parameter of interest. In particular, operation and maintenance costs are considered, along with economies of scale, which are typically disregarded in existing procedures. Beyond the interest of the results of the Shannon case study, the approach can be implemented in other regions with potential for hydrokinetic energy conversion.