We had a block that was too flat apparently. Cost us $3000 to get more dirt bought in, then another $500 to move the excess spoil 5 metres to the other side of our block (We are going to use it to fill in a corner). We also got pinged another $5000 for concrete piers.
Having said all this though we were advised that they have bought in fixed price piering, but in return they have upped the site costs. I think you will find though that all builders are very similar. Some of these costs aren't truly known until they get in there and do it. Check your contract and see if you have fixed price piering because that was the one we really didn't expect.