I understand why they charge so much. It takes a lot of time to finish a dented fender, even one that isn't rusted. Take their advice and get some after-market body parts or the rust will come back. I finally got a fiberglass fender for my 62 and I'm considering more. I wish that I had done so long ago. It would have saved me time and money in the long run. I bought from Chevyduty. Their metal fender sucked but the fiberglass one is much nicer.
