I have personally used the solution that easyrider83 refers to.
Take any of the universal input voltage converters you can purchase, and just apply DC to it. The bridge rectifier will always be working on a single direction, but so what?
This is not only the cheapest solution, it will provide an isolated secondary side from the primary voltage, and will save you a ton of time, expense and aggravation designing your own PSU (which is not trivial if you have never designed one).