Id say around 3-5K for a decent at most shops. Ive worked for a Used Car lot/Body shop for 3 years, We deal with rebuilts, and Wrecks. Some cars have under 1K miles on them. I really dont have any faith in Single Stage Enamel. Real-World Lifespan is about 4 years in good condition. Base/Clear is the only way I could see to go. We get away with spending about 70 on a gallon of clear and about 30 for activator. Generally a Re-paint of same color will take 1-2 quarts for a full-mid size car. Generally prices are anywhere from 90-160 a quart depending on the color.
Doing a complete color change, Door jambs, Hood, deck lid etc would all take quite a bit. I would estimate between a gallon to a gallon and a half of paint alone to do a color change. All depends on the paint. How dense it is. (P Test) Gun nozzle etc.
A gallon of reducer will run about 35$. Figure Prep materials of 400 Wet/Dry, Some gray scuff pads and some scuff paste
Not sure what your EPA laws are in your state. But down here they have been cracking down. Have to have a certified and inspected paint building with EPL lighting and EP Exhaust fans. Anyone caught spraying outside of a Buildijnng/Booth with a gun capable of holding more than 3 ounces is held liable for up to a $25,000 fine for both Sprayer and Owner.
We do occasionlly take on side jobs and do them for about half the price that a shop on-The-Clock would charge.