Anything that breaks in the interior of the car should be replaced no matter what you have to pay for it.
If you get it repaired you will feel bad about it and then the next buyer will also notice. This sort of repair shows signs of neglect and money saving.
Respect your car and go to a chop shop and get the air grill from them. Remember no matter how carefully you repair the grill it will still be noticeable.
No doubt about it. Get a replacement grill.