Walmart offers the K'Nex Son of Serpent Coaster Building Set for $552. Opt for in-store pickup to cut it to $435.38. That's $58 under our mention from month and the lowest price we could find by $65. This 5,000-piece kit stands over five feet tall and seven feet long when assembled. Also included are speakers for an MP3 player, 16 K'NexMen figures, five coaster cars, and three motorized chain lifts.