On the contrary, without a solid base of airline orders a new airliner isn't going to be built these days so there won't even be a certification process. I agree with your comment re. BOAC/BEA anguish but even there it was the builder rather than the customer which suffered the anguish.
Of course if there's a near-blank cheque, there's not going to be an overrun. Polaris was a National imperative and nobody was going to moan too much even if costs had risen. (That's if anyone found out; official secrecy would keep out any public or press snotty noses).