Very wide range high voltage measurement with optical isolation
If you're REALLY careful with your choice of parts, you can resistively divide the 1kV input into something you can read directly.  It won't be isolated that way, so you'd need to figure out some kind of protection in case a resistor comes loose or you drop a wire across it or something like that.  Maybe a sacrificial buffer amp?

If you use an active buffer between the source and the ADC, you can also apply some gain and offset so that the expected range to measure fills up the entire range of the ADC (with some headroom for out-of-range detection).  That might be a good idea by itself.