I have a water leak that I think is coming from the water pump. Is this a major repair job and very costly?

It can be a pain. Most water pumps are designed with something called a weep hole, which is a hole in the housing that is blocked by the bearing assembly. As the bearing wears, the hole is slowly uncovered, and when the bearing has worn to the point that it needs to be replaced, the weep hole is exposed and coolant can leak out - this is to tell you that the water pump is wearing out, and it forces you to change it before it fails and strands you, or worse, costs you an engine.

Shop rates vary widely, but since a water pump is usually replaced when a timing belt is done, you may want to step up and do that if you're anywhere near 60k miles (or a multiple of it, like 120k or 180k). If you have done the timing belt recently enough that it isn't a worry, you can have just the water pump and the belt that drives it replaced. Probably with parts and labor you'd be looking at $200-300 but I'd shop around for prices and reputation before turning over your car for this job, as it's not a small job. It's not a gigantic project, but it's not a tiny one either.