I'm sure that someone with more experience can post something more helpful, but from what I know, it's a bit of work. The water pump is in a rather strange place, and the mechanic needs to take apart several things in order to get to it.
When I had the head gasket done on my car, my mechanic looked at the water pump to see how it was -- it would have been really easy to replace it at that point. It was fine though, so he didn't.
Exactly what's involved, I'm not sure -- but someone will help with that.
Hope you're enjoying the NICE weather in Hawaii -- it's rainy and 40 here in Illinois! At least it's not SNOW!!