As for the water pump, an electric water pump for a small block engine is around $175.
$200 for a pwm controller? Your typical water pump is no more than 5A. You can easily have a 12v 10A for $10 to $20.
Granted, that PWM controller is manual control. The ideal system would be temperature controlled.
Here is a chip that's specifically designed for temperature regulated fan control. I don't see any reference to how much current it can drive, though.