You can break down the cost of painting a car, to the same tune as your other expenses and it will make sense to you, after you've budgeted how much time has been sunken into each piece of the process.
Up until May of this year, I was restoring cars for a living, full time for a shop.
We charged a minimum of $7k for body and paint, if the car needed any kind of rust repair, because of the sheer amount of work involved on a car.
I just finished assembling a new back half on a '70 AAR cuda. There was nothing, behind the rear window channel, except for frame rails.
I can tell you without any doubt, that AMD makes reasonable parts, but they are absolutely in no way, ready to assemble on to any car. The flanges needed cutting, a few parts needed adjustment and tweaking, like the decklid that had too much arch to fit the same contour of the deck filler, etc.
Once you've ground every spot weld and you have taken care of any hidden rust or other corrosion, you've got any ugly metal straightened back out and weatherproofed, you are ready to start tackling the task of getting those quarter panels aligned perfectly with the doors, deck filler, deck lid opening, rear body, etc.
When you replace full quarters, especially on both sides, you are looking at alignment on basically every single panel on the car, because it all follows the quarter panels, as they do not adjust once in place and you need to have enough adjustment in the hinged and bolted panels to get the correct gaps.
More often than not, even with brand new panels, gap adjusting with minor edge welding is needed to get a good gap.
To anyone trash talking a $10k paint job that includes the painstaking process of replacing full quarters or even rust repair patching;
If you think you can do it, do it yourself. This is not an insult. This is the mindset that I took on and that is exactly what I do. I don't pay. I do it myself. It takes some practice, but if you want to save the money, spend the time and get comfy with a face shield and earplugs. It is all nasty work. Sanding body filler is loaded with talc/ chalk and gets more airborne than sawdust. You will be wiping it out of your eyelashes and sweating pools, if you do it right, with a two foot longboard.
Its easy to forget when terms like "body shop prison" are used. People watch too much fuckin' TV and assume that its easy work or some sort of magic. No. It doesn't just take years worth of screw ups to know how to do it right with enough confidence to charge someone for it, it burns more calories than a PX90 workout. I lost 40lbs in 3 months doing a complete paint job, 2 years ago, over the summer. I clocked out at work and worked until 9pm every night for 3 months, until it was color sanded, polished and put together, and I didn't even have the task of full panel replacement.
Even though I had no major collision to deal with and only typical rust, I still had to remove every single panel, replace the hinge pins in the doors and do a ton of gap correcting, because the factory stuff was that ugly.
Pay the man his 10k or get ready for a trial of patience and your physical endurance.