This study uses a model of production and supply and demand for two input categories: purchased inputs versus owned inputs. A Cobb-Douglas production function is calibrated, along with supply and demand for inputs, to simulate the welfare impact of Mexico’s ban on genetically modified (GM) corn for human consumption, focusing on how the policy affects farms of different sizes. It examines three policy tools—input subsidies, production subsidies, and technological change—under fixed and endogenous output prices, while accounting for varying demand elasticities. Results show that input subsidies yield the most consistent producer surplus (PS) gains across all farm sizes, especially small farms. Production subsidies are also effective, especially when demand is elastic. However, technological change becomes less beneficial under the GM corn ban, as it limits its productivity-enhancing effect. Large farms, which depend more on inputs from genetically modified organisms (GMOs), face the most significant welfare losses. In contrast, small and medium farms benefit more from GM corn because it is a cost-reducing policy. The findings suggest a shift in policy from technological innovation to input-based and sustainable support, highlighting the need for equitable and environmentally adaptive agricultural strategies in a post-GMO context.