Body shops are fronts for the insurance companies. They are paid by the insurance companies and as such are insurance company employees that own their own tools. If they are going to work on your car it will be off the insurance companies pay clock so it will be after doing eight or more hours of sanding.
Also and this is the most important part they are used to doing collision repair not rust repair on cars where there is no sheet metal readily (cheaply) available, for an insurance company that wants to put as little labor into a repair as possible. If their isn't a new or cheaply obtainable piece of sheet metal to hang like sheet rock, they will slather on body filler rather than cut and remove a piece of bad metal.
The shop may not even have a MIG or TIG welder instead relying upon a 110V hand held spot welder to hang fenders. So they haven't the ability to weld in patch panels or fabricate a patch panel using a shrinker, English wheel, hand operated brake, or a seam roller. If they have the equipment the next question is who besides the owner knows how to use the metal working equipment.
I am not saying you have to go to a custom automotive fabricator to get your rust holes properly repaired, but you will have to find a shop with the time, equipment, and knowledge to properly repair your car at an economically justifiable price.
Restoring cars is a hobby usually performed by retired body men that used to know how and frequently used lead for filler material before plastic body filler was invented. If you can do the body work yourself you will save a fortune; that you can then spend on shop tools to repair your car, and your next project, and the car after that one.
Do not worry about the powertrain as that can be bought mail order for less money than the cost of the parts to build a motor or tranny (this I know first hand as I used to be an engine builder for race cars). They frequently come with a warranty that starts the day you buy it, not when the truck actually delivers your motor to your door(where you have to have a fork lift to remove it, or pay extra in shipping for a truck with a hydraulic lift tail gate). So there is no need to buy a shinny chromed motor for it to sit on an engine stand for years as you get your car ready for paint.