Question about the cost of electricity for 250watt mh/hps-or-400 watt indoor grow

HEY ALL. I'M A NEWBIE AND HAVE DONE allot of research, thus far, before I germ my first seed. I've been on, and studied the best practices-of many forums but have not seen the following topic directly addressed:
I am considering to use either a 250WATT or 400 WATT MH/HPS-(COMBO_ LIGHT KIT-FROM HTG) and I needed to know about the COST OF ELECTRICITY FOR AN AVERAGE(5 MONTH) GROW USING THE ABOVE COMBINATION OF LIGHTS FOR A GROW.
<<<<IN YOUR REPLY-PLEASE PICK ONE WATTAGE TO REPLY FOR>>>>>>>>>>>
-LET'S SAY-50% of the time will be spent using the MH light .then I'll swap bulbs and..........
The other 50% of the time I will use THE HPS LIGHT TO FLOWER-<APPR- 3 MONTHS+.
I, like many of my brethren, are concerned about the "TARGET-POINT" for electricity, at which the utilities will knock at your door.Am trying to avoid this-that's why I'm cosidering the 250WATT/400WATT lights.

CAN ANYONE GIVE ME A ROUGH IDEA ABOUT THIS ASPECT OF INDOOR GROWING?>For the sake of simplicity, let's say I WON'T BE growing HYDROPONICAllY-and-PLEASE specify WHICH wattage you are replying to-I would GREATLY APPRECIATE THAT.
PEACE ALL.......AND Thanks for the asssistance....
...........may all your plants thrive and flower

a 400w running 18hrs a day is only gonna cost you between $15-$25 per month, depends on where you live and what rates you pay.

My bill went up $30.00 a month using a 400 hps 18/6 and also running 2 small oscillating fans and one inline fan !

i dont know about anyone else but that really helped me, only problem is im not american so not sure what your typical electricity bills are, if there higher or lower then over here, put it this way, if you left your typical 40-60w lamp on 18 hours a day for a month lets say, how much will it cost you?

TO ALL WHO REPLIED=Thank you very, very much. This answer(as well as the formulae) is a HUGE help to me and I have to admit-this WAS the missing piece of the puzzle for me.

NOW all I must do is to "determine" the amount of electricity usage (In the USA) that will trigger the door-knocking, nosy FEDS.

Peace to all and may your "Buds outweigh your Cat"
Keep it Green........Free it all..............

I know a little old, but if you're running during peak times the cost is astronomical. If you run lights mostly at night, it will cost a whole lot less (atleast for my company)

Quality LED is the way to go, runs cooler too saving more energy

Renfro said:

Quality LED is the way to go, runs cooler too saving more energy

Click to expand...

I was looking into them, $300 to build 2x Cobs and can run them up to 250-364 watts a piece. Not the most efficient but just that will put up 60k lumen. Obviously more led spread the better but when on a budget, gott a do what you gotta do. This will be next upgrade.