Engine diagnostic code is PO171. How much should the work cost, parts and labor

Hello, which engine is your E150 equipped with? P0171 and P0174 are indicative of a "lean" running condition for both banks (both sides of cylinders) of the engine. This means there is a common failure that affects both sides -- so you'll typically look for a vacuum leak or an air intake leak. Depending on the engine, you could have intake gaskets leaking air, a PCV tube leak, or some kind of air tube / mass air flow sensor concern. Don't guess though! Professional testing is needed to determine the cause of failure. Unless you see an obviously failed part -- like a detached air box or broken air tube -- or broken PCV tube -- test first, then determine what needs to be repaired. (You could also have fuel delivery problems like a fuel pump or filter -- but these are less likely causes.) Good luck!