Amazon Prime Exclusive. Amazon offers the K'NEX 70 Model Building Set (705-Pieces) for a discounted price of $17.88 plus snag free shipping on orders above $49, or with Amazon Prime. Limited time offer. You save 55% off the price! That's the lowest price we could find. This has a 4.6 out of 5 star rating with over 430 reviews on Amazon. This would be a great Engineering Education Toy for ages of 7 and up. Great non electronic gift idea for Christmas.