When we did ours there was an approximate cost per square meter, to which you add the land cost. Not got a clue what that is now, but to put it in perspective, we just upgraded the main bathroom and spent almost exactly double the total cost of ALL our plumbing work when the house was built 13 years ago - and that included the leadwork on the roof, gutters and downpipes, mains water supply, two bathroom suites etc.

Expect to save about 1/3rd of the value of the finished house, if you do a fair bit yourself, less if you contract it all out.