Some paint is lost as my car slid into a post recently. Can I paint the definite portion where paint is lost, or do I have to paint the whole side?
Costing questions are off-topic for this group, so can't answer that.
I'm not a refinisher, so can't give a gospel answer with full details, but how much of the car has to be repainted will depend on the age of the car - i.e, how old/dull is the existing paint, the extent of the damage, and the finish on the paint. Flat tones are easier to blend in than metallics, and newer paint on the car will be easier to blend in with a repair. If it's an older car with dull paint, consider t-cutting the entire side of the car (or the whole car), then painting the repair area; the blend will then be closer to the original paint color.