Target offers the K'Nex Robo Smash Building Set, model no. 13243, for $11.19 with free shipping. (Walmart and Amazon charge the same via pickup and shipping, respectively.) That's the lowest total price we could find by $2, although we saw it for $3 less last December. This 156-piece set requires two AA batteries (not included), and once it's constructed it hops around like a primate.