Bio-based plastics, produced from natural and renewable sources, have been found to be good replacers to petroleum-based plastics. However, economic analyses have not been carried out for most of them, specifically those from whey. In this study, a techno-economic assessment of the industrial-scale production of plastics from whey protein is carried out considering two different scenarios: (1) low-cost dairy waste whey (DWP) and (2) purchased whey protein concentrate (WPC), as feedstocks, using SuperPro Designer software. Key economic indicators such as operating cost, capital investment, annual revenue, payback time, and return-on-investment (ROI), were analyzed. Sensitivity analyses of different parameters were performed to account for market fluctuations and other uncertainties, using Scenario 2 as the base case. Results showed that both scenarios have the capacity of producing over 3200 metric tons/year (t/yr) (or 5.5 t/batch) of plastic. With the unit selling price of plastic set at $7,000/t, both the scenarios showed profitable outcomes with the plant’s payback time of 3.7 and 2.4 years, and ROI of 27.1% and 42.2%, for Scenario 1 and Scenario 2, respectively. Sensitivity analyses showed that the unit plastic selling price was the most sensitive parameter, followed by the amount of feedstock WPC, and the number of batches.