In this paper, for the first time the application of nanofluids is investigated from the point of view of thermoeconomics. For this purpose, the mixed convection flow of Al2O3-EG nanofluid in an isothermal vertical annulus is considered where three sets of models are used to calculate the viscosity and thermal conductivity of nanofluid. The main aim of this work is to estimate the operational costs ($) due to entropy generation using nanofluids in the annulus. The results show that using nanofluids is not cost-effective in short periods (i.e., 5-6 months) from the point of view of the second law of thermodynamics. In future works, besides the entropy generation, changes in the heat transfer rate that occurs using nanofluids, and their effects on the costs, can be considered.