Some method of spraying paint is probably the first hurdle. The preparation for many repairs can be done by hand if there are no grinders, sanders or other time-saving power tools are available, but the final steps need some means of applying primer and topcoats to a decent standard.
Very small localised repairs can be carried out to a reasonable standard using aerosol primers and paints, but anything larger will require a compressed air supply and some type of spray gun.
Small compressor units can now be bought quite cheaply - around £100 should find a small direct-drive unit, possibly even with a cheap and cheerful spraygun and accessory kit. With air output between 5-8cfm this sort of hardware is quite suitable for spraying panels and part resprays, though it would probably be rather slow for larger projects.
Note that sprayguns supplied in these accessory kits tend to be very basic, but reasonable quality copies of professional guns can be bought cheaply - just take note of the air requirements of any spray gun you buy. If the air cap set up is too large for your compressor the air supply will run down almost immediately, especially if the air receiver (tank) is small.
Keep in mind that while these budget compressors are ideal for occasional diy use, they are not really intended for continuous heavy use. More detailed information about air compressors on this page.
Profession and semi-professional compressors are available in much larger sizes, both in air output and air storage capabilities, and also tend to have hardware which is heavier duty and slower running.
Note that most larger compressors (above 3hp / 14 cfm) will need a three phase 440 volt electrical supply, so for domestic use the size of compressor you can use will usually be limited by the electrical supply at your workshop.
Car Body Repairs Tools and Equipment