Boo boo on my CAR

[Conn SVX]

My sister in law was driving my car on the Mass pike last year, she claims she hit a tool ( a pick axe ) that some road crew left behind in the road or it fell off the truck. Anyway it flew up scrapped the side of the car ( I managed to rub out all the Yellow paint) but when it got to the rear wheel it caught the wheel well. This is the only dammage I have on the car, My Question is how do I fix it without replacing the whoe rear of the car : Autobody suggestion est $600.00