The price of feedstock is one of the most significant factors affecting the economic viability of biodiesel manufacturer. Many approaches were investigated to reduce the biodiesel production cost. The present work gave a preliminary study of two approaches to economically produce biodiesel from waste cooking oil (WCO) and flaked cottonseed. One was the use of ultrasound-assisted synthesis of biodiesel from WCO. The other was the application of in situ transesterification from flaked cottonseed. Gas chromatography (GC) and High performance liquid chromatography (HPLC) results demonstrated the feasibility of using both approaches to produce biodiesel from low-cost feedstock.