How much could it possibly be to replace the plumbing in a 1k square foot house?

It's not that big of a house. The previous owner's stripped the copper piping from under the house. (that's another side question.. isn't copper only found in older houses?) I have some friends in this business that will work for $10/hr to get the work done. But how long could it possibly take? I can finance all the supplies that will be needed.. just the labor is starting to freighten me. The place has all of the fixtures. They are a bit outdated.. but I'll get around to replacing them later.