Mechanical engineering students at Brigham Young University used off-the-shelf components to make a wheelchair for less than $500. It weighs just over 20 lbs.

The frame of the chair is made of PVC pipes with a battery under the seat and two electric motors power the front wheels. An armrest-mounted joystick allowing the kids to navigate wherever they want to go controls the device.
The whole device weighs just over 20 lbs. Less than $500 used to construct the wheelchair using off-the-shelf components, a considerable savings compared to commercially available motorized wheelchairs.
The students will soon be releasing the list of the parts and the construction plans for the wheelchairs, allowing anyone anywhere to build inexpensive motorized wheelchair.
Source-Medindia