However, if you happen to have access to a laser cutter, you may be able to build your own Nybble for free. The cat is entirely open source — you just need to be able to cut the pieces for its wooden frame.
Once the cat is built, you can program it to do a variety of things including walking and playing. Additionally, you can add a computer chip like a Raspberry Pi once the cat is built so it can do more complex things and maybe even start to think a little bit.