To replace the entire plumbing in a house will vary as to how big the house is and how much work is involved to completely redo the plumbing in the house.
But lets say your house is 1,500 square feet, with an average cost of $4.50 per square foot you can expect to pay $6,750.00 to completely redo the plumbing in the 1,500 square foot house.
And of course if you need other things such as faucets, toilets replaced etc then the cost can be even higher.
Let's just say that if you hire a plumbing company to completely replace all the plumbing which includes the gas lines, water lines, drain and sewer lines etc that it will not be cheap to get it done.