It seems a lot of people are a little hesitant when it comes to painting their own car. Although it may seem like a daunting task, with a little practice it isn't all that difficult.
This post isn't meant to be a tutorial on painting but to show what is possible in your garage.
First you have to construct a temporary paint booth. Not as difficult as you might think. What I do is take some 2x2 lumber and screw it into the ceiling of my garage in the shape I want to enclose. Then I staple plastic sheeting to the 2x2 and let it drape to the floor where I duct tape it down. I also build a small door out of scrap wood and a couple cheap hinges sheeted with plastic so you can get in and out easily and still seal it.
Venting is important and I use standard house fans (with brushless motors). Because they are brushless they create no sparks once turned on and pose much less of an explosive risk than most inexpensive fans.
If I'm painting an entire car and the booth is large I'll use two intake and one exhaust. If I'm doing something smaller I'll use one fan on high for the intake and one on medium for the exhaust. I also try to locate the intake where it will pickup the least amount of dust and the exhaust somewhere on the opposite side of the boot to create a cross flow. Venting in this manor creates a positive pressure booth and keeps the plastic from moving every time you walk buy it. I also found that a typical furnace filter is enough to eliminate most dust from entering the booth. It's my experience that you'll never get rid of all the dust when painting in a garage so spending a lot of money on filters just doesn't make that much sense.
Also check to make sure the exhaust vents to the outside of the building. If you have an attached garage you don't want the fumes getting inside the house and you don't want them being sucked back in the intake either. Venting outside isn't hard. All you have to do is build a duct out of the same plastic you used for the walls and once the exhaust fan is turned on it will inflate and carry the fumes outside. In my case I raised the garage door about 2 1/2' and vented it there.
Finally, never paint using urethanes or any paints requiring hardeners without some kind of breathing equipment. I use a Hobby Air pressure breathing system and would feel safe using anything less with these paints. ISO's can kill you and catalyzed paints are loaded with them so use a good breathing equipment.
With a little practice and decent equipment (gun, compressor and breathing), almost anyone can have excellent quality results. Sorry but these pics aren't the best quality... probably because they were taken at 6:00 AM this morning and I was still half asleep. I removed one wall of the booth for the benefit of the camera. The paint was PPG Omni MTX acrylic urethane Single Stage (1969 Dodge Hemi Orange). Tack coat, two color coats and a final coat mixed 50/50 with PPG fast clear using a Sata gravity feed conventional gun.