The electric powered, 2.4GHz radio controlled, ready to fly Proto X Nano quadcopter from Estes, is the smallest you can find around.
LED light indicates front and back of the heli, and also helps in low light flying
Plastic body with window and trim detail
4-channel 2.4GHz Radio with digital trims
Four micro motors
100mAh 3.7V LiPo battery
USB charge cord
One-piece PCB frame
Available for $40 here
Due to its very small size, the Proto-X has a built-in LiPo battery that is not designed for replacement.
Attempting to remove or replace the Lipo battery will likely damage the quadcopter.