Make This a Constructive Challenge
Usually, you have to be extremely well placed to win a battle with consultants who have influence with the CEO. They are usually very skilled at managing their stakeholders and securing their fees because that is the lifeblood of their business. If top management has brought them in, chances are they are highly experienced at managing internal resources and protecting what they believe to be their delivery objective. So, you need to think carefully before tackling them in an adversarial manner.
It is easy to lose motivation as the consultants move in with their high fees and even higher confidence levels. Letting your emotions take control will move you further away from resolving this dilemma. You need to resist this temptation and try to establish within your mind an objective pursuit of the best outcome for all concerned.
The consultants have been engaged with a legitimate mission to accomplish. What often is forgotten is the longer-term health of the organization in which they are unlikely to have any real interest. If you can meet with them in constructive dialogue and make connections between addressing your reservations and their gain, so much the better.
The way you approach them has a big impact on the regard they show for you. If you are critical of their ideas, scathing of their methods, and bitter about their fees, then you are setting yourself in opposition to them. You are more likely to succeed if you can find genuine good ...