One reason it may have cost you more could have been time of year. Power companies charge different rates depending on the time of year. And they commonly "estimate" your power bill in winter months in such a way as it can cost you 3 or 4 times what you actually use. I have this fight with my electric provider every year, where they estimate a $300 power bill when the actual meter reading will result in only an $80 bill. A lot of people try MHs for the first time in the winter and experience the sticker shock--people generally don't do MHs until they think they need them, which is when Mr. Sun has decided to take a vacation from the northern hemisphere.
The problem here is that you are comparing apples and oranges. 400W is 400W for input. The same is not true of output. According to National Garden Wholesale in order to get 50,000 lumins, you need either a single 400W HID lamp or 10 4ft 54W T5's or 42 4ft 40W T12's. [http://www.nationalgardenwholesale.c...plemental.pdf]