If you have some extra cheap servos and an Arduino you can use them to make this open source quadruped RobotQuad. It was developed by Regis Hsu and as open source project and its design is updated frequently. It should be a very affordable thing to build as all the servos needed will cost some 20 USD.
In the linked Instructable there are also possibilities to make a remote control unit and IR obstacle detection.
Here is the version 3.0 whit some dance music:
Detailed build instructions can be found at:
Hari Wiguna made a video about his build:
I really like the DIY aesthetics of this robot: