Natural convected heat transportation attributes can be elaborated better using entropy generation analysis. In current framework, we scrutinized magnetized Al2O3-H2O nanomaterial natural convection based on entropy generation and L-shaped cavity. Non-dimensional forms of governing expressions are computed through Control Volume-based Finite Element Method (CVFEM). Entropy generation number is calculated. Features of active parameters e.g. Rayleigh number, nanoparticles volume-fraction, nanoparticle shape, Hartmann number, magnetic field angle and aspect ratio versus average heat transportation rate (Nusselt number) and the entropy generation number are investigated. For the first time, an economic analysis is introduced for evaluating the performance of the enclosure with consideration cost of nanofluid. Also, in order to assess the performance of the enclosure, six criteria are introduced which two of them are based on the cost of nanofluids. The results were compared with references and a good compromise was seen. According to the results, both the entropy generation number and average heat transportation rate rise when Rayleigh number upsurges. The average heat transportation rate rises with ascending the nanoparticle volume-fraction whereas the entropy generation number declines when nanoparticles concentration ascends. The entropy generation number decreases 15.14% and 8.15% for Ha=25 and Ha=75, respectively, when ϕ increases from 0 to 0.1.