I think there is a lot of myth about MH and driving up the power bill. As with all systems, it is the wattage and the duration of the light use that is significant. Running a pc/t5/vho might be more expensive than running a MH for a shorter period, but once again that is personal choice. MH may cause you AC to work harder, but you may save a bit in the winter since they are small heaters. I know my MH work in the mild SC winters
well, for the specific MH question, I am running two Hamilton 400DE and my power bill is stable and I have yet to trip the breaker. Total bill for my home is less than $80 a month for electricity (as low as $55 some months), but thats the SC kWh rate of $.069 too. I run them 4 hours each with one firing 1.5 hours before the other so it is 6.5 hours of run time total.
If you just want to have enough light for a nem, I would suggest to spotlight it. Have one MH for over the area of the nem and have pc/t5 or vho. I think hellolights were running assembled 250w pendents for $215 recently. If you look around, I am sure you can find a good deal. Overall, I feel that MH are better for growth and shimmer, but I am a sps person overall and I know that there are issues with heat and such.
... just food for thought