K’NEX Firestorm Freefall Coaster Building Set ONLY $19.97 This post may contain affiliate links. Please see the full disclosure policy here. Posted on November 27, 2013 Written by Mary Leave a Comment HOT PRICE! K’NEX Firestorm Freefall Coaster Building Set is ON SALE at Walmart today! Grab it for ONLY $19.97. Hurry over before the price goes back up!