Cheap, small air compressors don't cut it for painting or sanding a car.
Most of your paint guns uses 7 to 14 cfm of air @ 90 psi, Same with most sanders and grinders
Small, cheap air compressors only put out 2-5 cfm @90 psi.
Air compressors, welders, etc are not tools to cheap out on.
You said you work on cars alot. Will then save up and get a good, big compressor. It will make your life 100% easier. Tons more use for a compressor other than painting.
I use mine daily. My air tools are
Impact wrench, air ratchet, die grinder, 4" angle grinder, riviet gun, blow guns, paint guns, air saws, 3" cut off tool, air file, sheet metal nibbler, drill.
By using tools like air impact and ratchet it makes all of my auto work go twice as fast as normal.
I have an Ingersall-Rand 60 gal, 240 volt, 11.3 cfm @ 90 psi compressor. Had it for about 8 to 9 years now. When I bought mine I got it for $425, now the same ones are $500-700 depending on where you shop. Well worth it.
As far as painting goes, you do NOT want to have to play keep up where you have to sto to let compressor catch up and re fill the small tank every few min.
Even with my 60 gal, 11.3 cfm compressor, I can only get 1/2 to 1/3 of the way through painting a single coat on a car before the compressor gets on and has to refill tank..
Which thats ok, cause thats also about the same time I have to re fill my paint cup on spray gun.
The more the compressor runs the hotter the air will get in the tank, the more water that will be in air, the more risk of paint flashing too soon due to hot air or getting water sprayed through gun and paint.
You will also need 3/8" or 1/2" air line (depends on how long of a run you have) My setup has 125 feet of line so I use a 1/2" size.
You will need an adjust air reg., water trap, filter.
Harbor freight is a ghood place to buy your reg/filter/water trap, air lines and fitting and even spray gun.
I use and love their #43430 purple HVLP gun. As someone already said it's a knock off of the older sata guns