High voltage LED indicator 40-1000 VDC without additional power supply
Connect a moving coil analog voltmeter across the power bus. 

Either a voltmeter as shown with internal series resistor or an external resistor
and scale calibrated for the desired range. Photo from this useless site. 

Old-school suppliers such as Crompton should be able to supply a meter with the markings you need, if not a turnkey solution.