Walmart offers the K'nex SuperSonic Swirl Building Set for $14.99. (Amazon charges the same for Prime members.) Choose in-store pickup to dodge the $4.97 shipping fee. That's the lowest price we could find by $7. This 464-piece set includes a motor and figure.
Need it for Christmas? At Walmart, upgrade to standard shipping for $6.97 and place your order by December 19.