I picked up this model kit from AMAZON when I was in the United States recently. It is an inexpensive kit, priced under $10.
I have always been interested in the works of Dutch Artist Theo Jansen, especially his StrandBeest moving sculptures, and this model is a great way of gaining understanding of how the mechanics of the legs function.
The model is easy to assemble, taking me under 40 minutes to complete, requiring no tools or glue and once assembled the model functions surprisingly well. The one complaint I do have about the kit is that the provided instructions are not always easy to follow, this is in part due to the very poor English translation.
Even given this fact, I would still recommend this kit, not only because of the learnings it provides in walking mechanics, but also as it looks really cool when completed and to top that off it is really inexpensive as well.