I would suggest that you seriously look at the modules of the types shown in this catalogue page:

http://www.astrodyne.com/pdf/ASD03.pdf

If you look at the model ADS03-48S5M you can anticipate a module capable of producing 5V @ 500 mA from an input of 36->72volts. A benefit of these units is that the output is isolated from the input.

For quantities of 10+ this device is listed on their web page at $16.00 each. http://www.astrodyne.com/astro/pro...5&x=12&y=8

There are also ways to build your own circuit using switching supply components from National Semiconductor but for your low quantity I would go with the Astrodyne modules.

Michael Karas