get a balist you can switch form mh to hps. then you just need two bulbs. I did this for awhile but had to wait to long betwen grows/harvests.
I've grown with CFL's
Currently growing with HPS and MH
If you're only going to buy one of the two HID lights go for the HPS it will be better for the over all grow than the MH. You absolutely can't beat the HPS four flower.
From personal experience CFLs are alright, but there's nothing light the HID bulbs for growing weed. If you want to grow some serious weight you'll need HID. My set up when i was using CFLs was four 27 watters in soil, stealth rubbermaid tub, no nutrients, no real care, and i got about 2 gram per plant. At the time i was really growing for the pure novelty of it and wasn't serious in the least bit.
The switchable digital ballast is a great idea if you have the money. All the equipment is the same for both lights other than the ballast. As for the 1000w compared to 600w... the 600 watters are more efficient overall than the 1000 watters (more lumens per watt)
On the electricity front it's really simple to figure out what your electricity usage is. Here's a formula:
(watts of light/1000) x Time(amount of hours the light is run for a month) x KWH rating (it will be written on your electric bill) = cost to run light for an entire month.
To give you a reference point i use 250w of light and it costs me a little less than $12 a month to run. 250w is less than most tvs well probably not the new flat screens anymore.
oh and led's they're not there yet. i'll get into for you but thats for another post.
GL
Oh and ps. if you're looking for a small set up that could suffice for two moderate smokers or so check out my grow in my my grow room album in my profile. I've also got a brand new journal... link's in my sig