To be precise, one has to distinguish M601D (or earlier versions) from M601E/F. D-s are less powerful, consume less fuel (150 lph on an L-410, though it would obviously be more in Ag operations), and are considerably cheaper to maintain (by 30-35%), but you won't find a new one except from someone's old stash. E-s and F-s are being officially produced, but I am not sure if Walter is really making new ones rather than selling its old stock. Generally, the demand nowadays somewhat exceeds the supply, driving the prices up.