Repair panels are definitely available and you may even find an NOS piece. Camaro is the same which makes it easier. I think the body work should cost $300-$500 including parts. Paint would be about the same amount because you would have to paint the whole rear of the car because there is no place to stop with a paint line seam. Body shops are hard to predict so the total cost could vary from $500 to $1500.
Jim