Walmart offers the K'Nex Revvin' Race Car 2-In-1 Building Set for $18.74. (Amazon charges the same with free Prime shipping.) Opt for in-store pickup to dodge the $5.99 shipping charge. That's the lowest total price we could find by $6, although it was $4 less in November. The set includes over 370 pieces to build two cars. It requires two AA batteries (not included).
Walmart offers the K'Nex Tinkertoy 65-Piece Essentials Value Set for $14.49. Opt for in-store pickup to dodge the $5.99 shipping charge. That's the lowest price we could find by $3. This set includes spools, rods, flags, washers, end caps, and building ideas for seven models.