Man this thread blew up. Must be the click bait title.
If you go DIY you can most certainly build a cob setup for 1300 or less. If you are wanting to cover a 4x4 you could buy something like this already put together.
Or you could buy all the components and put them together for around a 1000. Hell, I bet this light would do you pretty well.
http://timbergrowlights.com/900-watt-vero29-v7-5x5-framework/ You could buy all the components and put it together yourself for a lot less.
It's hard to figure the exact metric, but I can tell you when I was running DE hps in the same room the bill was about 75-100$ more than it is now. My bill has gone way down this summer of all things when its hot as fuck, stays nice and cool in the room and my A/C doesn't come on near as much. Not to mention the increase in yield.