Auto body repair & detailing: Collision repair estimate, rear quarter panel, us postal service

Question
I have a 1984 GMC K-1500 4x4 short bed pick-up. I was broad sided by the US Postal Service damaging the right rear quarter panel of the box.

I went to several local body shops for an estimate without success! They just don't want anything to do with it because of the age. However, the truck is in pretty nice "solid" shape other than a couple of small rust spots.
They tell me it can turn into a nightmare on something that old when you go to replace the panel.

Here's my dilemna: The US Postal Service is self insured! They will not pay me for the damage with out an estimate detailing the parts, labor, etc.

Would you be able to tell me what you would normally charge to replace the right side rear quarter panel, all the labor cost associated with it and the re-painting of that area of the truck?
I also had to replace the gas tank and brackets because it shifted the box enough on collision to rupture the tank. I have the parts receipts but what would you charge in labor for doing that? It took me about 1-1/2 to 2 hours to do the work.

Thank you very much as it will be greatly appreciated!! Wish more folks would do what you guys are on this site! Wish you the best!

Answer
They are right,as much as it sucks to hear, it will cost to much to fix. The thing with rust is it's like cancer and spreads to what it's attached to. The only thing you can do is cut it all out and even then it's not a sure thing.You just need to hunt around for someone to write the sheet for you. As far as cost, it all depends on pars price,labor rate of the area etc...Sorry I can't say for sure but It is 20 years old.