My dog chewed up the door panel on my 2001 deville. She bit the leather right under the rear left window.

I have had to replace the rear door panel before and the dealer charged me $1003 including installation and tax. Now a different dog did the same thing to the same door! Can this be fixed without replacing the whole door panel?

If the door panel has to be replaced where can I buy one cheap?

Check with an upholstery shop and see if they can just replace the leather. I'm sure they can for much cheaper than replacing the whole panel!
And feed your dog once in a while, so it doesn't eat Cadillacs! :)