Walmart offers the K'Nex Son of Serpent Coaster Building Set for $518.85. Opt for in-store pickup to knock it to $505.88. That's $494 off list price and the best deal we could find by $13. (However, most stores charge beyond $600.) This 5,000-piece kit stands over 5 feet tall and 7 feet long when assembled. Also included are speakers for an MP3 player, 16 K'NexMen figures, five coaster cars, and three motorized chain lifts.