air filter box clips failing and box replacement on 2008 Chrysler Sebring

My clips on the air filter box went bad, I told my dealer that I needed them replaced and/or repaired. Gave them a coupon for 20% off repair price, they came back and told me their was stated that it didnt need repair. Now my box is broke and dust got in my engine. I think my mechanic caught this on time before major damage was done although some damage has occured. My question is how much is the box going to cost. And is the dealer liable.
I am really upset with them they should have fixed it when I asked the first time.

Asked by for the 2008 Chrysler Sebring