Webbs1200, I am definitely pro electric pumps, however, I do disagree with you about the amount of load the alternator produces.

The alternator will have to produce extra output (total amperage) to operate the waterpump, this in turn will take a little of the horsepower from the engine.

As I mentioned before, energy cannot be created or destroyed, it can only be changed, so the power needed to drive the water pump has to come from somewhere. And before you say it, if the power is supplied from the battery, how does the battery get recharged?

As for $/HP gained, you'd be surprised how little rotating mass you need to removed to get a decent HP gain.

There are also a heap of other factors to take into account like the inertia of the coolant when accelerating, it all adds up to extra HP at the wheels.