Are you prepared for the recurring costs?
Energy - Large tanks will need plenty of light exposure to cover the surface area of the water. Lighting hardware are expensive to purchase, and expensive to run for eight to twelve hours per day. If you live in California, you really understand this fact. Powerful lights like metal halide lamps generate a lot of heat--enough heat to actually heat up the tank.
If the heat is too great, then you'll need to keep it cool with a chiller. It's just like fighting both sides of a war. As you can expect, chillers aren't cheap, and the compressor uses a fair amount of electricity. Heat can also be kept in check by using a fan to blow air over the sump; however, this results in increased evaporation.
Water - To combat the evaporation problem, you'll need to have plenty of deionized water on hand. That means lots of jugs of DI water, or a well designed DI unit. Reverse osmosis/deionized water can be purchased at your local fish store, or can be filtered at home. Most RODI units run about $200-$300. DI water can be purchased for about $0.50 per gallon.
Likewise salt water can be purchased or mixed yourself with your own DI water and salt mix. Consider a budget of no more than $1.00 per gallon for saltwater if you purchase it.
Light bulbs! - Oh yeah, these ain't cheap either. Metal halides bulbs can run anywhere between $85 to $250 per bulb depending on the type. You should probably change these out every 9-12 months. Fluorescents cost about half as much but you need to change them twice as often as metal halide bulbs in order to maintain the proper frequencies of light.
Fish food - You've got hungry mouths to feed. Fortunately, this isn't a great expense. Costs can be reduced further by making the food yourself.