Lots of people have asked about buying BRAINS for personal use. Unfortunately, they are not currently available and, nationally speaking, there is a shortage. In future years, production rates may be high enough to make them available for sale...but not for a while.

You might be interested in picking up a servo-motor control board and going from there. Here is a typical link
http://www.trossenrobotics.com/c/usb-serial-robot-servo-controllers.aspx

Note the robot kit area of that website for some ideas of what is available...