Trouble with these kits is that servos are pretty expensive - though when you think about it they ARE quite nice position-controlled motors, so I don't see a decent way to drop the price without buying your own low-ratio gearboxes, encoders and doing lots of microcontroller programing.
I just did a search and found one of those fairly expensive dinosaur ones, stripped down. Quite a lot of electronics in there! I have no idea what it's using for position encoders (if anything). All in fun:
I guess as a minimum two legs could be done with 4, 5 or 6 servos, maybe...