Halide help

well most people only run their halides for a few hours so im sure the cost insn't to bad. with a 140 i would run 2 250 watt haides either mogul or double ended bulb or even 2 400 watt mh.

What are the length and depth of the tank? I'd suggest one lamp per 2 ft of tank. If it's deep, like more than 24", I would definitely suggest 400 watt lamps.

The cost depends on your point of view. You get more light per watt than any other lighting system, and as Stephen pointed out, they tend to be on for fewer hours than fluorescents.

Dfish, you can do an estimate on the cost by comparing the wattages of your lights-if you put 2 250w halides on, run them for 4 hours a day, that's 2 kilowatts a day of electricity use-look at your light bill to see how much you pay per kilowatt. It will probably list it as kw/hr (kilowatt/hour or kilowatt hours).
HTH

much of it depends on what you are going to keep. Watts/gallon is an older method of lighting specs. the best way is to judge the PAR value for the specific ballast and bulb combination you plan to use. The higher the K value (in general) the bluer the light and the lower the par, also depending on magnetic or electronic balast, reflector and bulb brand can impact the quality of the light.
Think like this if watts/gallon were a good measure then why doesn't a 500 watt pc fixture work well enough to grow sps simply put the par (light intensity) reaching the bottom of the water is not high enough to grow them.