Talk to as many builders as you can. I got in my own soil test/footing details ($330) and my own contour report/features ($450) and also got in my own site cost quote plus quote for crushed limestone access way. Not only will builders quote horrendous site costs, they are "Provisional Sums" and not even fixed, so a builder can still exceed them.
Builders will say the standard HIA contract is "fixed cost" and that is bovine excrement.