If you need to find cheap DC motors for your projects, it is easy. DC motors are used in many different electronic devices. You can salvage DC motors on your own or purchase cheap surplus DC motors removed from old electronics equipment.
Find some old CD players or computer CD drives. The iPod has made these devices virtually obsolete so many people are now disposing or selling their old CD drives very cheap. CD drives are a great source of cheap DC motors since they usually have at least 2 sometimes up to 4 (muli-disc players) DC motors.
Find some old computer cooling fans. Computer cooling fans are typically brushless DC motors with a quiet ball bearing fan attached. Unplug the old computer and open the case. Inside you might find a case cooling fan, a CPU cooling fan, and a power supply cooling fan. All these fans are typically DC brushless motors that operate on 5V or 12V.
Salvage larger industrial size DC motors from home items such as a clothes dryer, treadmill, and car starters. These motors are usually brushed DC motors. They are much larger, more powerful and use more energy.
Go to goodwill or garage sales to find electronic toys. Some toys such as cheap remote control cars, cheap toy robots and other toys with moving parts use DC motors. You can find these toys for as little as 50 cents.
Find some old VCR players. VCR's are now all but considered antique. If you can find some that are being throw away, they are a great source of DC motors. Many times the VCR will not function properly, but most if not all of the DC motors in the unit will still work great. Find some VCR units to add some cheap DC motors for your project.
Search for "electronics surplus" on your favorite search engine. There are many good electronics surplus stores online. Electronics surplus stores such as electronic goldmine, alltronics, and H&R surplus carry cheap DC motors for your project. This is another great way to find cheap DC motors since you just pick out what you want.