High rama108
A 630 would do nicely but I would prefer two 315s so I had the option of just using one at a time if I didn't need full power. Cost a lot more I imagine tho. You would have better coverage in a 4x5 with two smaller lights than one big one as well.
I use CFLs and now a DIY LED bulb rig for vegging small plants then up the power to a 400W MH until they get a nice size then into the flower room under a 1000W Hortilux Super HPS. Wishing I had a 600W to fill the gap but I get by.
I have 3 - 400W HPS ballasts as well as the 400MH and 2 - 1000W. One MH only and one MH/HPS. All are older magnetic coil and core ballasts.
Power is expensive here too so if I had no lights I'd probably be doing a DIY COB setup. Lots of good info here how to do it and they save a lot of juice and still grow great pot. My flower room is down in the basement where it's always cool so I don't need A/C which saves a bunch. That's something for you to consider as well.
I'm not sure about the 315s whether you can get the separate parts or have to buy the hood/ballast combo units. I prefer separate parts so the hood is much lighter and I can have the ballast outside the grow room to cut down a bit on heat. I often use my light rail to extend the area a light can cover and tho it can handle the weight it should last longer with just a lightweight open hood and bulb hanging off it.
With the CMH you have both a grow and bloom bulb in one so you save a bit there. If you get it, get a spare bulb too if you can. Sux waiting for a replacement if a bulb blows.
I found a great spot to download
FREE POT BOOKS. I downloaded a grow bible first and got lots more. Books look great and complete like the real ones I have here. No web site but just a page of links. Just right click on what you want and then "Save Link As" to download so they don't open first as some are 50+ megs. They got lots. Enjoy.
Good luck and good growing!