Wouldn't an indoor pond be suitable? Just build a frame with cinderblocks or lumber, then put in a pond liner...you would need a pond filter and heater as well, but it would be cheap and easy to make a big enough tank that way. I'm planning to do that when I have the space!
) than say a 2ft cichlid, arowana have very large scales so still need alot of space to move, you also have to take into account that a arowana can move at 1 hell of a speed.