Do you really have one single AC source that can vary that much? If so, and you ultimately need DC, the better thing would be to making your own Very Wide Range AC to DC converter. But, as ronsimpson said, such a converter won't be cheap. But it may likely be cheaper than an AC voltage regulator.
Or are you trying to make a single product that can be used in a variety of different locations. The locations may be 120, 240, 480, etc, but each location stays in it's own range. If that is the case, I would suggest a multi-tapped autoformer as your front end. Then just connect to the appropriate tap for a given location.
Questions:
1) What DC voltage and current do you actually need at the output?
2) Is this a one-off need, or is it a production item?