The standard contracts handle this pretty well; it's not a surprise that surprises happen. In commercial projects, this often triggers an arbitration about the

The standard contracts handle this pretty well; it's not a surprise that surprises happen. In commercial projects, this often triggers an arbitration about the overrun. You get experts to challenge the fairness of the price, hopefully using market data. And, of course, there are the courts. In worst case, the buyer can cancel and/or rebid. Not 'competitive,' but adversarial.