Next to most of the US Western all the SW were low Budget Western. I'm not quite sure but I think The Good, the Bad and the Ugly, Once Upon a Time in the West, Duck you sucker and My Name is Nobody had a higher Budget as usual in the business. I don't think that Corbucci or Sollima ever had the same budget as Leone in Duck you Sucker or Once Upon a Time in the West. Fistful of Dollars is the cheapest of the Leone Movies (I think even his peplums had more budget!) but it worked perfectly. I don't have any numbers to compare but Fistful of Dollars must be one of the cheapest but most successful in the SW Business.