Walmart offers the K'NEX Firestorm Freefall Coaster, model no. 51539, for $19.97. Opt for in-store pickup to dodge the $4.97 shipping fee. That's $2 under our expired mention of a shipped unit from two days ago and the lowest price we've seen. (It's a current low by $33.) This 674-piece set features a motorized chain lift, 18-foot track, and it requires two AA batteries (not included).
Walmart offers the K'Nex Tinkertoy Big Top Building Set, model no. 56538, for $27.97. (Amazon charges the same for Prime members.) Choose Site-to-Store pickup to dodge the $4.97 shipping charge. That's the lowest price we could find by $13. Among the 188 pieces are spools, rods, flags, washers, and end caps.