Meet the ROBOTIS Darwin-Mini robot: a humanoid robot you can build and program to get started in robotics. It has an open source embedded board and supports R+ Task and R+ Motion. It has 16 Dynamixel XL-320 servos and 3D printable frames. You can control the robot from your smartphone. Adding additional modules to upgrade it is also an option.
The Darwin-Mini robot is available for under $500 at this time.