<p>Magnetic nanoparticles (MNPs) have enhanced the removal of pollutants from water to circumvent the drastic effects on the environment and living organisms. Despite their extensive application in water remediation studies, little is known about their cost analysis. This study comprehensively and critically discussed the different techniques utilised to evaluate the cost analysis of magnetic nanoadsorbents. Fifty-five research articles were selected after employing a systematic inclusion and exclusion criterion. In the studied research articles, about 76% employed the cost of adsorbent preparation economic evaluation method, 15% utilised the cost of adsorption per volume of sample, and 9% of the studies used the cost of adsorption per gram of adsorbate. The study highlighted methodological heterogeneity in cost analysis and identified gaps and challenges in standardising the cost evaluation techniques, which prevent accurate comparison. Moreover, this study demonstrated that the adsorption cost can be significantly reduced by regenerating the adsorbent; for instance, in one study, the cost was reduced from 0.38 to 0.038 USD due to ten-fold reusability of the adsorbent. A worked example demonstrated ways to accurately determine costs and significantly reduce the costs of treating contaminants from water. This included employing the adsorption cost method, incorporating easily accessible waste materials to MNPs, selecting less energy-intensive synthetic techniques, preparing stable materials to ensure reusability, and using industrial-scale costs. As this is an emerging area of research, this study provides a standardised, step-by-step framework for estimating the costs of pollutant removal from water systems, with relevance to policymakers and real-world industrial applications. Clinical trial number: not applicable.</p>