I am really scared of that
With the ground, there are really only two things that can get expensive: rock and water. Both can be fairly well ruled out with a soil report. If it can't be ruled out, you have to set aside an extra budget. So have a report made; usually the fear is unfounded. With us, we knew in advance that we could hit rock, and we did. Money was set aside, so no problem. Of course, I would have preferred to keep the money.