Amazon offers Prime members the K'Nex Robo Smash Building Set, model no. 13243, for $7.59 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it adds $6.18.) That's tied with our mention from a month ago and the lowest total price we could find by $6. This 156-piece set requires two AA batteries (not included), and once it's constructed it hops around like a primate.
Of note, Target has it for the same price with in-store pickup.