Some of the national guys run 6 to 10 150W units at 100% over a tank your size, so I was just curious where you came out with your personal analysis. This helps me a bunch, thanks, since I like to pay attention so that I know when it will be time for me to switch.
If it helps you out any, I have 6 250W HQI burning for 8 hours and the bill on this is about 1.20 a day. If you cannot afford this kind of dough, then any hobby, let alone this one, is probably not going to work out too well.
Also, anybody considering a real cost/benefit analysis using LED also has to consider the cost of new panels - the idea that panels last for 10+ years is a joke. As fast as LED units are progressing, there will likely be many people that will have bought all new panels by the time that you need to replace your MH bulbs.