As the owner of a large vintage automobile restoration shop, allow me to weigh in a little. To begin with, ...all is not lost at this point, but there are some things you need to discuss and you potentially need a 3rd party mediator.
The part about the paint being wavy is because they used the buffer with a heavy compound instead of block-sanding (wet-sanding) up to a minimum of 3000 grit before touching it. For the record, on our concours paint, we actually use 5000 grit. My point is it is likely fixable to a certain extent, but let me move on.
Approach the shop with a rational & calm demeanor and explain that you have seen other restored vehicles that do not have the sand scratch marks, so ask them 'Do they feel they can do better?'. If they say No, then just share with them that new vehicles do not have those marks nor do other vehicles coming out of your shop, so is it truly the 'best of their ability"?
Now as far as the marks go, I would probably hand block (-not a DA) each panel on the entire paint job with 240 grit to get under the clear, and then gravitate to 320 and then 400 grit until we are down to the top of the primer substrates. The reason you do not want to just block-sand the top-coat is the Mil thickness will be too great which will make it prone to chipping. Get it back down to the substrates. When they get to this point, you want to come inspect the work. The best way we have found to inspect on fine-point concours is to use a florescent drop light to inspect the finish. We load a spray gun with Wax & Grease Remover and spray a coat onto the panel to make it wet. The portable lamp will hi-light imperfections where they can be noted and corrected. The easiest way to note them is to use 3M 5861 guidecoat and just daub a little over that area. Then come back and block that area again and repeat the Wax & Grease spray.
I hope this has helped some. It honestly is not the end of the world. Most people just do not realize that while a restoration shop and a collision shop both paint automobiles, there is night & day difference between the two methods. Most shops that do concours level of paintwork do not give estimates. If this shop did, that may be where the trouble originated since they realized they underbid and were just trying to rush the job. And for the record, with heavy sheetmetal work and other things besides paint, $20k may be light on costs in today's market. Changing quarters and/or doing heavy floor panel replacement to a concours-level can easily take half of that $20k on some vehicles.
