“I have no problem with someone turning down an ED offer for any other university that is indeed lower cost for them to attend.”
That completely breaks the terms of ED. No one is forced to apply ED. Breaking ED can harm later students at that student’s HS, as it makes the counseling staff look incompetent or duplicitous.
And I don’t believe NPCs are off by thousands and thousands of dollars. I am skeptical that a parent would run the NPC and expect to pay 10K, and then the cost is 50K per year. The actual cost for D17 was within a thousand dollars (less) than the EFC we had calculated.