It might be worth pointing out that the cost of the tank is the one of least expensive parts of this hobby IMO. 400+ gallons of reef will require some substantial pumps and lighting depending on what you are going to keep. Not to mention, the cost of livestock to fill it up.

Not to talk you out of a 400 gallon tank, cause I'd love to see you build it and post it up on our site. However, if cost is an issue at this point in the game, you may want to price out everything and make sure you know where your going.