Cheap but time consuming
Cleaning materials aren't very costly. Canned air, alcohol, cotton balls, cotton swabs, and maybe machine oil for printers are all relatively cheap. The cleaning process, however, can be very time-consuming.

Cleaning the PC
Attack your PCs first. The electricity in the machine generates a static electric charge that attracts a lot of dust. Dust bunnies can bind up power supplies and interfere with the flow of electricity to vital connections.

When cleaning out a PC, remember to blow the dust away with compressed air. Never use a vacuum cleaner because they generate their own electric charge. (You run the risk of shorting out your computer when you turn it back on if the charge generated by the vacuum hasn't dissipated.)

Start by moving the machine to a suitable cleaning location, usually away from other people. Depending on the computer's condition, length of service, and physical location (on the floor is always better for raising dust bunnies than on top of a desk), your efforts may raise a dust cloud that others wouldn't want to inhale.

Next, remove the case to thoroughly clean the PC. Leaving the case on could result in spreading dust from the power supply to the rest of the internal areas. Pay special attention to the power supply. Use all of the various air openings to force the dust out. Finally, clean the PC's exterior and all exterior openings. Be sure to clean the floppy drives, which can store lots of dust since they are not used as much as they once were.

Those pesky peripherals
Once you've finished cleaning the actual PC, turn your attention to the often forgotten peripherals and accessories. Clean the surge protector. Most surge protectors lay forgotten on the floor. Dust bunnies, popcorn, even paper clips congregate around surge protectors. The dust that accumulates there could cause a fire. Disconnect the surge protector from the wall outlet and blow it off before reconnecting the PC.

Tackle the keyboard next. Paperclips, staples, hair, and food can collect beneath the keys, preventing them from working properly. Blow the debris away and wipe the keys with an alcohol swap or alcohol-dampened cotton ball. When you return the unit to the end-user, they may feel like they're getting a new one.

Next, turn your attention to the mouse. Remove the mouse ball and work on the tiny bars inside the mouse casing. You will need a small, slender object to remove the caked-on gunk that has accumulated there (sometimes you can scrape it with your fingernail). Finish up with an alcohol-dipped cotton swab.

Finally, wipe off the monitor's screen and casing with a clean soft cloth and a little glass cleaner. If you're cleaning an LCD screen, be careful not to press on the screen too hard.

Don't forget your printers
Printers are often overlooked during PC cleaning time, but they need a little bit of care as well. Different kinds of printers need different kinds of attention. You should refer to the manufacturer's instructions before diving into the guts of the equipment.

Laser printers should be blown out each time the toner is replaced. Many printers come with the ability to clean themselves. If yours do, clean the print heads according to the manufacturer's instructions.

Impact or dot matrix printers require more frequent attention but a can of air is all that you need. Blow away any dust and leftover paper dots. This debris can cause malfunctions or misread indicators. You may also want to dab a few drops of oil on the bar of older machines.

Cost benefit analysis
As with any task, you have to weigh the costs against the benefits. Cleaning can be time-consuming, but it can stretch the life of your equipment. Longer life means less frequent service or replacements. Less-frequent service equals less downtime and less-frequent replacements equals a lower bottom line.