I back into my usual parking spot at lunch today and I noticed a trail of coolant underneath the engine. For the life of me I cannot tell where it is coming from. It is basically running down the oil pan trickeling onto the ground while the engine is idling. The radiator is bone dry, hoses leading into and out of the radiator are dry. The overflow res is dry (not cracked). My thoughts are the water pump or heater core neither of which I can visually locate/see. I only ran it a couple of miles, temp gauge is registering in the normal range. The cooling system still has some fluid in it as when I start it it starts to leak again. Radiator is not full of coolant anymore. Engine did not appear to overheat. Power - fine, no noises.

Any thoughts?

How much too replace the water pump? What is entailed in that job?