Walmart offers the K'nex Hyperspeed Hangtime Roller Coaster Building Set, model no. 51415, for $29.99. (Amazon charges the same for Prime members.) Choose Site-to-Store pickup to avoid the $4.97 shipping fee. That's tied with last week's mention and the lowest price we could find by $22. It features over 620 pieces and is recommended for ages 9 and above.