Per month for 600 watt

Well first you have to find out how much your electric company charges..they do it by kilowatt per hour. It's either on one of your electric bills, their website or you can call them.

The Kilowatt per hour is a huge factor in this, so much so that the national average (12 cents) cost $29.38 for 12/12 600 watts for 30 days. But if you're in a place that cost like 20 cents kw/h then it would be $48.96

I forgot the formula exactly and I don't want to give you wrong info, but if you read this before other replies find out what your company charges for kw/h and find out the watts of everything that will be in your grow room..Then one of the nerds can do it for you..But thats info that IS needed. Providing those things would not give you an 'estimate' but will indeed give you the EXACT amount of money it will cost.

 

Take a look at your electric bill, find out how much you pay kw/h, then google utility calculator.
problem solved

 

You wouldn't want or need to use that HPS for veg, unless its a digital capable of using both MH and HPS in it. Otherwise CFLs or Floros tubes would be better and save a shit ton on electricity. I googled the average cost for kwh in California and it said 20 cents

So according to this graph(which is actually showing for 680 watts), for 20 cents kw/h..So I really hope you're not paying 20 cents per kilowatt..because that really sucks for you. In that case, you're much better off using CFLs to veg ^_^

18/6 for 30 days = $73.44
12/12 for 30 days = $48.96

Running it 20-4 would be a waste, I do believe most growers unanimously agree that theres no difference in growth or rate of growth while on a 20-4 or 18-6..So you're better off running 18-6 to save on the bill

 

Thing is, If I recall you said you would be growing 3-4 plants..600 watt MH for that many plants in veg isn't needed at all. I'd much rather just got some floros and veg under those, unless you're wanting monster plants before flipping or a really long veg time. Hell the amount of money you would save vegging with floros would basically pay for themselves in 30 days :S Saving 30ish dollars a month is a decent amount. But if your ballast is digital and you have the MH bulb, already than go for it. Technically its just 2 hours less, so thats like 4 bucks..Cutting down by two hours wouldn't save all that much, but as said, you're getting nothing out of it 2 hours extra adds up, in 30 days thats 60 hours extra thats pretty much not needed. Which is indeed cutting the life expectancy of your bulbs/ballast down. As said, 2 extra unneeded hours doesn't sound like much, but it does indeed add up..If you can squeeze just one more harvest before having to break down and buy a new bulb that saves you money..I guess im looking at it from a penny pincher view. I mean, you're living in an area with a RIDICULOUSLY HIGH electricity costs. Electricity bills will no doubt be your most costly thing in your grow :S hell if I were living in a state with that high of bill, i'd fucking veg them outside wrapped in a small screen to prevent bugs :S

But yeah, I strongly recommend you just veg with floros, or if your ballast is dimmable, which would be awesome, just crank it out to 50% and that will be good enough

 

My rate in cali is 13 cents...live in the city tho not suburbs and no im not on reduced pge rates...which I wish I was lol...