If it were truly unaffordable and based on what OP wrote that is clearly not the case but if it were, it would be appropriate to discuss with the fin aid ASAP as they meet need (yes as they define it).
But stating x school costs less is not a reason to do this nor will they care.
That said NYU is publicly more flexible with cancelling ED than others.
It’s too bad when this happens - someone else was or will be likely WL and had a dream crushed.
I know - the student is just a teen - but the rationale is laughable. It’s not - NYC has changed or my love for it changed and I want suburban. And what happens if the UC is Merced or Riverside. Is this another - if I get into UCB/UCLA ?
It’s - I booked a non refundable rate at the Marriott but the Hilton just launched a promo and I can save 30%. How do I get out of it ??