I have painted numerous cars in my garage.
The biggest factor is the prep work and no, I will not paint over someone else's prep work.
I have had guys come to me with cars they say are "ready to spray" only to find substandard work and materials. The paint job will carry my name on it so even if the paint fails because of something the other guy did - when people ask "who did the paint?" it will be my name that is given.
This truck came to me after another shop had "painted it." They quickly painted everything in pieces and charged the guy $6000.
When I got it there were bent parts, broken off screws, bolts, worn out holes and cracks in the paint. One crack in the front fender was deep so I sanded down through 1/2" of filler to find a substandard patch job that still had rusted metal in it.
The color for this truck was $800 a gallon and that did not include primers, clear or reducer.
The next truck shown was painted by a "custom shop" in California just two years prior to coming to me.
Notice the cracks in the paint:
I ended up stripping this entire truck.
The body and prep work was horrendous. Here is a chip of the paint removed. Notice how thick the filler is under it.
This was mess was under the paint on the bed side.
Stripped and prepped properly and then repainted:
Here is one last example of what people pass off as acceptable.
1965 Buick convertible.
Here's what was underneath:
Bondo over 1" thick.
My point being that you can find someone who will "paint" your car cheap but somewhere they will be cutting corners.
Material costs alone can run close to $2000 for quality products that will last.
So the bottom line is what is the car worth to you? Granted some classic cars are not worth the money invested in them so a cheap paint job may be in order. However when dealing with a car that has value or even personal value it is best to ensure that it is prepped and painted properly IMHO.