The net-zero emission target necessitates a significantly expanded deployment of clean technologies compared to their current utilization. Precisely estimating the future potential of these technologies requires a thorough understanding of their cost and carbon footprint evolution. This study bridges the gap by integrating life cycle assessment (LCA) and cost estimation methodologies, resulting in a comprehensive bottom-up model that simultaneously evaluates the cost and carbon footprint, with particular attention to the scaling effect. This model is then applied to scrutinize the manufacturing processes of Proton Exchange Membrane Electrolysis Cells (PEMEC) and Solid Oxide Electrolysis Cells (SOEC). The assessment incorporates a detailed manufacturing process description and equipment inventory. It is found as manufacturing capacity increases, both the cost and carbon footprint decrease. Notably, at a low manufacturing capacity of 1MW/year, SOEC exhibits higher costs and a greater carbon footprint compared to PEMEC, with values of $900/MW and 110,000 kg/MW, respectively. However, SOEC's advantage lies in its superior scaling performance, attributed to more cost-effective and environmentally friendly raw material inputs. These results are leveraged to forecast future costs and carbon footprints of PEMEC and SOEC, offering valuable insights for further decarbonization of green hydrogen production.